DEFINING AND BOUNDING SLAVERY

Given its presence across hugely diverse political and social settings over the millennia, the nature and practice of slavery differed widely. Our working definition is that slavery is a formal relationship whereby one person or institution owns another as property (Reid Reference Reid and Reid1983, 2; Nieboer Reference Nieboer1910, 5; Lovejoy Reference Lovejoy2012, 1). According to this understanding, slavery lies at the extreme end of a continuum of unfree labor. It is nevertheless different from the many other kinds of related but distinct practices on this spectrum, including serfdom, indentured servitude, pawnship, court eunuchs, and penal colonies. Different categories of unfree labor might perform somewhat equivalent roles in different social contexts, for example, nineteenth-century slaves in East Africa compared with serfs in Russia in the same era.

Reflecting this continuum, many scholars have called for a broader definition of slavery that would include some or all of the other categories of unfree labor (for definitional discussions, see Eltis and Engerman Reference Eltis, Engerman, Eltis and Engerman2011; Stilwell Reference Stilwell2014; Eltis et al. Reference Eltis, Engerman, Drescher, Richardson, Eltis, Engerman, Drescher and Richardson2017; Zeuske Reference Zeuske2017; Reid Reference Reid and Allen2022). Others have argued that the term “slave” should be abandoned, because it is inevitably associated with American plantation slavery, and does not do justice to contexts and nuances beyond the European Atlantic. Yet most specialist historians of slavery in African, Asian, and Native American societies still agree that slavery is the appropriate term to describe local practices and arrangements, that slavery is distinct from other forms of unfree labor, and that there is utility in being able to make comparisons across time and place, even while acknowledging vital regional differences (for the Native Americas, e.g., Santos-Granero Reference Santos-Granero2009, 3–5, 225–7; Snyder Reference Snyder2012, 3-5; for Asia, e.g., Reid Reference Reid and Reid1983, 1–3; Stanziani Reference Stanziani, Eltis, Engerman, Drescher and Richardson2017, 246–9; Toledano Reference Toledano, Eltis and Engerman2011, 30–3; for Africa, e.g., Lovejoy Reference Lovejoy2012, 1–2; Stilwell Reference Stilwell2014, 1–11). We agree. Finally, in addition to fuzzy definitional boundaries, there are important differences within the category of slavery. Some scholars have distinguished “open” systems in which slaves are gradually assimilated into the dominant population from “closed” systems where slaves are strictly separated from the dominant population across generations (Watson Reference Watson1980; Reid Reference Reid and Reid1983). Rather than engaging in an abstract typological discussion, however, we theorize different expressions of slavery in their historical contexts.

POLITICAL SCIENCE AND THE STUDY OF SLAVERY: NEGLECT AND BIAS

Enslavement of human beings by other human beings is one of the rare global practices that is transculturally and transhistorically commonplace (Reid Reference Reid and Reid1983; Patterson Reference Patterson1990; Eltis and Engerman Reference Eltis, Engerman, Eltis and Engerman2011; Klein Reference Klein2016; Eltis et al. Reference Eltis, Engerman, Drescher, Richardson, Eltis, Engerman, Drescher and Richardson2017; Pargas and Rosu Reference Pargas, Rosu, Alan and Rosu2017; Fynn-Paul Reference Fynn-Paul2022). Slavery existed in all continents and periods up to the twentieth century (and continues to exist informally today). As such, legacies of slavery occur almost everywhere. If these legacies now seem more visible in some settings rather than others, it is incumbent on us to explain why, instead of generalizing only from better-known episodes (Ince Reference Ince2022).

To the limited extent slavery has received attention in political science, it is almost always taken as synonymous with the Atlantic slave trade, whereby Europeans shipped captive Africans to the Americas (e.g., Kaufmann and Pape Reference Kaufmann and Pape1999; Keene Reference Keene2007; Shilliam Reference Shilliam2012; for exceptions, see Lowenheim Reference Lowenheim2003; Blaydes and Chaney Reference Blaydes and Chaney2013). This is unsurprising, given that until recently the study of slavery in history has also been subject to a “tyranny of the Atlantic” (Allen Reference Allen2022, 1; see also Allen Reference Allen2014, 108; Pargas and Rosu Reference Pargas, Rosu, Alan and Rosu2017, 9; Stanziani Reference Stanziani, Eltis, Engerman, Drescher and Richardson2017, 246; Toledano Reference Toledano, Eltis and Engerman2011, 44; Ware Reference Ware, Eltis, Engerman, Drescher and Richardson2017, 346; Zeuske Reference Zeuske2017, 249). This strong association of slavery in the modern era with the West and European colonialism is a by-product of Eurocentrism. At the same time, this is a rare Eurocentrism that suits most parties (Allen Reference Allen2022, 2). Non-Western states are hardly clamoring to claim their place in this shameful historiography. But the stories of people enslaved by non-Western actors also deserve to be told, and their impact on creating the world we live in also needs to be recognized. Aside from this geographic bias, coverage of slavery disproportionately analyzes slavery in economic rather than political terms (Robinson Reference Robinson2002, 518; Toledano Reference Toledano, Eltis and Engerman2011, 44; Bennett Reference Bennett2019, 6, 11). Taking a more comparative view of slavery can help us better theorize key political science concerns.

The general neglect of slavery in the discipline, and the American-Atlantic skew in the study of slavery elsewhere, means that even relatively recent large-scale incidences of slavery—and their significance in theoretical and conceptual terms—remain unknown. The European conquest and settlement of the Americas was built on the Africanization of the New World; before 1850, five in six of those crossing the oceans to the Americas were African slaves, not European settlers (Inikori Reference Inikori, Akyeampong, Bates, Nunn and Robinson2014, 70). But it is also important to realize that millions of other people have been moved around the world due to enslavement. Sub-Saharan Africa supplied not just the Atlantic slave trade but also that of Asia: “an estimated 10.9-11.6 million slaves” from the region went to “the Mediterranean, the Middle East, South Asia, and Southeast Asia between 650 and 1900” (Allen Reference Allen2022, 15). Slavery within Africa long pre-dated European contact, and actually expanded after the abolition of the trans-Atlantic trade (Austin Reference Austin, Eltis, Engerman, Drescher and Richardson2017, 176).

Slaves were also procured from all other continents, including Europe. Until the middle of the seventeenth century, there were probably more Europeans enslaved in the Islamic world than enslaved Africans in the Americas (Eltis and Engerman Reference Eltis, Engerman, Eltis and Engerman2011, 16; see also Davis Reference Davis2003). Thus, “Eastern Europe from the Caucasus to Poland-Lithuania was second only in numbers to sub-Saharan Africa as a source of slaves; between 1475 and 1694 it provided between 1 and 2.5 million slaves sold mainly in the Black Sea, Mediterranean, the Near and Middle East and Central Asia, not counting those who did not survive” (Stanziani Reference Stanziani, Eltis, Engerman, Drescher and Richardson2017, 2). Perhaps another two million Europeans were enslaved by Muslim pirates in the Mediterranean (Allen Reference Allen2022, 14). In the other direction, “an estimated 6.0-6.4 million Central Asians were trafficked into the Black Sea region, the Mediterranean world, and the Ottoman Empire between the eleventh and the nineteenth centuries” (Allen Reference Allen2022, 25). There were probably more slaves in British India than in the U.S. South in the mid-nineteenth century (Campbell and Stanziani Reference Campbell, Stanziani, Eltis, Engerman, Drescher and Richardson2017, 227). Slavery was a fundamental part of most of the states of Southeast Asia (Reid Reference Reid and Reid1983; Scott Reference Scott2009). In Korea, “approximately 30 percent of the indigenous population was held in bondage between the eleventh and eighteenth centuries” (Lovins Reference Lovins2022, 190).

In political science and International Relations (IR), what little work there is on slavery tends to concentrate on abolitionism (e.g., Kaufmann and Pape Reference Kaufmann and Pape1999; Crawford Reference Crawford2002; Klotz Reference Klotz2002; Lowenheim Reference Lowenheim2003; Keene Reference Keene2007; May Reference May, Owens and Rietzler2021; Shilliam Reference Shilliam2021). In this restricted focus, the field inadvertently reproduces misleading racial stereotypes where slaves have only been African, and masters European. In keeping with a more general neglect of the world beyond the West, it is only the agency of white Europeans and Americans that is center-stage. Discussion of the legacies of slavery up to the current day focuses on the United States and perhaps Western Europe, but hardly at all on the huge variety of non-Western societies that either practiced widespread slavery or were the sources of slave supply (categories that often overlapped) (for an exception, see Nunn Reference Nunn2008). When we expand our vision to the global scale, however, the relationship between slavery and its legacies becomes much more complicated, the historical relationship much more varied, and the implications for present-day politics much less straightforward. We point this out not to downplay the significance or violence of American slavery, nor to minimize its present-day impact. Nor are we engaging in “whataboutism.” Rather, we are pointing out that our understanding of even that (justifiably) well-scrutinized U.S. and Atlantic experience can benefit from a better grasp of the global historical practices of slavery. We now turn to substantiating the claims made in the Introduction regarding the importance of slavery for key political science questions.

SLAVERY AND STATE-BUILDING

In this section, we focus on the role of slavery in state-building via two trajectories. In the first, rulers employed slaves to compensate for and sometimes transcend the strictures of indirect rule in composite polities, in which the ruler’s administrative and military power relied upon sub-rulers who enjoyed considerable autonomy in pursuing their own interests. In response, slaves were used within the state apparatus, as officials and/or soldiers, because of their social isolation from competing groups, and their correspondingly undivided loyalty to the ruler (at least in theory). Slaves thus facilitated political centralization and the consolidation of state administrative and military power, constituting an alternative route to state-building than the over-studied European trajectory (Blaydes and Chaney Reference Blaydes and Chaney2013). The second aspect of state-building focuses on the political economy of slavery. Most commonly associated with the slave plantations of the Americas and the Caribbean, the slave economy also existed in Africa and Asia (Scott Reference Scott2009; Lovejoy Reference Lovejoy2012; Stilwell Reference Stilwell2014). Here the productive and reproductive labor of slaves was essential to the reproduction of the state. Much of the economy was based not on Pareto-improving bargains between free agents but instead on domination. The state could directly appropriate labor, in addition to taxing production. The slave economy was directly sustained by state power, while the state itself was sustained by slavery.

SLAVES AS THE STATE

The idea of powerful slaves who were armed, perhaps even members of the elite, may seem like a contradiction in terms. Yet from West Africa to the Middle East to South Asia, many kingdoms and empires were built upon the basis of slave armies and slave officials. In the Ottoman and Safavid empires, and earlier Sahelian African and Mamluk polities in Egypt, Iraq, and Northern India, slaves were crucial politico-military cadres and the major instruments of centralized rule. Beyond the Islamic world, slaves played an equivalent role in many African states (examined below), while slave soldiers were also commonly used from the ancient Mediterranean to the Mongol Empire, but also by European colonists around the world (Brown and Morgan Reference Brown and Morgan2006; Wyatt Reference Wyatt2022). Though Western European rulers faced the same problem of centralizing composite states, because of the atypical disappearance of intra-European/Christian slavery in the Middle Ages (see Heeboll-Holm Reference Heeboll-Holm2020), they did not use slave administrators and soldiers (the story in Eastern Europe, especially in Muscovy/Russia, was more complicated; see e.g., Hellie Reference Hellie, Eltis and Engerman2011; Witzenrath Reference Witzenrath2016). The lack of European historical experience with slave-based state centralization has translated into a theoretical neglect of this path.

A key problem of state-building for rulers in medieval and early modern periods was the fissiparous and composite nature of their domains (Ruggie Reference Ruggie1983; Nexon Reference Nexon2009). Rule and resource extraction was a highly mediated exercise in which local sub-rulers played an unavoidably prominent role (Tilly Reference Tilly1992). Rulers often had very little direct access to or control over “their” populations, most of whom owed their first loyalties to sub-rulers. Relations were often organized on the basis of the payment of tribute from component parts to the political center. Military forces often reflected the composite nature of the polity, being the private armed retainers of nobles who owed strictly limited loyalties to the central ruler. The composite nature of the polity and the military meant that polities were prone to fission and disintegration when sub-rulers seceded or transferred allegiance to other overlords at times of hardship or danger (Scott Reference Scott2009; Herbst Reference Herbst2014). Nominally supreme rulers looking to strengthen their hand against unruly subordinates needed soldiers and administrators with undivided loyalties.

Though this problem (and its solutions) has long been studied in European state formation (e.g., Weber [1919] Reference Weber2004), the fact that non-European rulers faced a similar problem has got less attention. Some non-European polities centralized more and earlier than their European counterparts (Zarakol Reference Zarakol2018; Reference Zarakol2022). One way they did so was through the use of a deracinated military and civil stratum of slaves to balance or neutralize local powerholders within composite polities. Slaves were sourced either by direct military predation, that is, a regular conscription of slaves imposed on subject populations (often by taking children to be raised as wards of the state), or as captives bought from slave producers elsewhere via long-distance slave trades (discussed below). Being wrenched from their social context, usually without families and highly dependent on their masters, slaves often formed an invaluable power-base for rulers independent of their often unruly nominal subordinates. This applied to the ruler’s slaves serving in court and the bureaucratic apparatus, but also in the construction of slave military forces that were exclusively loyal to the ruler. Thus across the Islamic world, “[m]en of slave origin often were drawn into the highest ranks of the sultan’s advisers, emissaries, and generals because their isolation from local politics and networks of patronage made them reliably loyal” (Miller Reference Miller and Miller2009, 238; see also Blaydes and Chaney Reference Blaydes and Chaney2013, 22). Similarly, in both Islamic and non-Islamic Africa, “[b]y using slaves, rulers created a professional body of officials within patrimonial and non-bureaucratic structures” (Stilwell Reference Stilwell2014, 109).

This use of slavery was most prevalent in Islamic polities, with the designation mamluk. Crone calls the invention of the mamluk institution almost a historical accident in the ninth century; facing revolts from competing houses, the Abbasid dynasty tried to solve its legitimacy crisis by creating servile armies of foreigners (usually not-yet-Muslim Turks). The logic of creating such an army was that they remained dependent on the ruler: “The combination of cultural dissociation and personal dependence was a very forceful one in that it obliterated the soldier’s public personality…the ruler would bring up his foreign slaves as his children, and they existed in the Muslim polity only through him…Mamluks were not supposed to think, but to ride horses; they were designed to be not a military elite, but military automata” (Crone Reference Crone1980, 97). The mamluk institution was then taken and modified by subsequent post-Abbasid Muslim polities, most significantly in the Mamluk, Ottoman, and Safavid Empires. In some of these subsequent arrangements, the slaves essentially took over the state, as in the Mamluk Sultanate in Egypt.

Perhaps the most important manifestation of “slaves as the state” model was the Ottoman Empire from the fifteenth century until the mid-seventeenth century. During this time, slaves constituted the most formidable military formation under Ottoman command and their most potent instrument of conquest, the janissaries. In addition, many of the most important civilian administrators in the empire were also slaves. Many of the Sultans’ top officials were former Christians who had been enslaved, forcibly converted, and then brought into Ottoman service. As a result, the Ottoman ruling circles had a notably cosmopolitan (though mono-religious) cast.

Originally Ottoman armies were largely irregular cavalry motivated by some combination of religious fervor and the prospect of booty (Agoston Reference Agoston2021). Among them were also non-Muslims (Darling Reference Darling2000). This loose model of political and military organization made it relatively easy to incorporate nobles transferring their loyalty to Ottoman rulers, but also limited the control of the center. The early Ottoman polity can thus be thought of as a “negotiated” or “brokered” frontier state (Barkey Reference Barkey2008). Initially, the Ottoman Sultan was more primus inter pares among the heads of other houses. From the fifteenth century, however, the empire began to centralize. The frontier nobles (akıncı) progressively lost power to the central court, especially to the Sultan’s slave and eunuch officials, who were disproportionately non-Turkic (Inalcik Reference Inalcik1954, 105; Antov Reference Antov2017, 3–4). The Sultan could increasingly check and dominate his nobles thanks to his slave retinue (Inalcik Reference Inalcik1954, 121–2).

Ironically, in the early decades of the empire, it had been the akıncı raiders who had procured these slaves for the court (Schmitt and Kiprovska Reference Schmitt and Kiprovska2022, 517). However, the process of enslavement became increasingly institutionalized through the devshirme system, according to which boys from the Christian Balkan subjects of the sultans were enslaved, forcibly converted, and put into imperial service. Around 200,000 boys were enslaved in this manner from the mid-fifteenth until the mid-seventeenth century (Barkey Reference Barkey2008, 124).

The growing empire was increasingly run by a cadre of devshirme slave bureaucrats and soldiers. Aside from the janissary corps, many served in “the administrative and military structure of the Ottoman state (as kapikulus, slaves of the Sublime Porte)” (Sobers-Khan Reference Sobers-Khan, Perry, Eltis, Engerman and Richardson2021, 417). At times they rose as high in rank as Grand Vezirs (equivalent of prime minister). Externally, the janissaries—who had eclipsed the akıncı raiders by the mid-fifteenth century—proved to be a highly effective instrument of Ottoman conquest in Europe and the Middle East, helping to build an empire that ran from Poland to Sudan and from Budapest to Baghdad (Agoston Reference Agoston2021). The importance of the janissaries and the slave administrators in the Ottoman elite demonstrates how slavery can function as an alternative path to “modernity” very different from that in Europe and the Americas, at least if conceived of as the move from a composite polity based on personalistic ties to a more centralized and (rational-)bureaucratic rule (Toledano Reference Toledano, Eltis and Engerman2011; Ferguson and Toledano Reference Ferguson, Toledano, Eltis, Engerman, Drescher and Richardson2017).

Even in their heyday, however, some formerly Christian Ottoman slave elites seemed to have maintained some residual loyalties to their ethnic kin (Kunt Reference Kunt1974), so the model did not work fully as intended. The decline of the janissaries is also instructive. From the mid-1600s they were no longer taken as boy slaves, but were increasingly recruited from the free Muslim population on a hereditary basis (Aksan Reference Aksan and Lee2011, 150). As a result, they became more socially and economically integrated as tax-farmers, but also less militarily effective and much less politically reliable than their predecessors, staging repeated rebellions against the sultans (Aksan Reference Aksan2007, 49–53; Barkey Reference Barkey2008, 206–9, 216–8; Agoston Reference Agoston2021, 321–3).

In the Persian Safavid Empire, slaves (ghulam) were similarly used in key military and administrative posts from the reign of Shah Tahmasb (r. 1524-76) onward. Once again, expanding the reach of the court via these deracinated slave bureaucrats and soldiers, who at least in theory had no allegiances except to the sovereign, allowed a greater degree of centralization in by-passing local powerholders (Toledano Reference Toledano, Eltis and Engerman2011, 37). They became increasingly powerful in the seventeenth century: “At the height of ghulam hegemony, the post of grand vizier was held by the eunuch Saru Taqi (1634-45) and all key positions in the military and financial structure were occupied by the slaves” (Babaie et al. Reference Babaie, Babayan, Baghdiantz-McCabe and Farhad2004, 11). The expansion of the slave bureaucracy checked the power of the tribal notables who had first supported the Safavids’ rise to power, and later vied for control by trying to influence the princes (Babaie et al. Reference Babaie, Babayan, Baghdiantz-McCabe and Farhad2004). In both the Ottoman and the Safavid cases, then, centralization of rule relied on the mamluk institution to build an administrative apparatus and standing professional army directly linked to the sovereign.

Many non-Islamic African rulers took a similar path to entrenching their authority: “Slaves played a central role in the reproduction of African states; slavery became essential to the continuation of state institutions and the political elite…They served as reliable bodies of dependents who facilitated political centralization…by providing bureaucratic continuity in systems that were otherwise outgrowths of households and lineages” (Stilwell Reference Stilwell2014, 91). Slaves were particularly valuable in this regard because African domains were even more fissiparous than the early Ottoman and Safavid polities, given that low population density forced extensive reliance on highly autonomous sub-rulers (Hacker Reference Hacker2008; Herbst Reference Herbst2014). Slavery had a long history in Africa well before European contact, with most slaves being outsiders taken by force, and hence lacking local social or kinship ties. Again, at least in expectation, slaves’ sole loyalties could be directed to the ruler: “elites often thought that the same dependency and kinlessness that made the slaves valuable administrators could also make them obedient soldiers” (Ware Reference Ware, Eltis and Engerman2011, 59). As in China and the Middle East, eunuchs were especially valued in this regard as “the ultimate outsiders” (Stilwell Reference Stilwell2014, 97). A further parallel was that African slave armies “often marked a move towards increased centralization and autocracy” (Ware Reference Ware, Eltis and Engerman2011, 60; see also Hacker Reference Hacker2008, 70). Slave armies were used internally to check the power of the nobility at least as much as against external enemies (Thornton Reference Thornton1998, 91).

Slave soldiers were prominent in non-Islamic Africa from Ethiopia and the Portuguese Zambezi valley in East Africa, to Kongo, Ndongo, Dahomey, Oyo, and many smaller polities in West Africa (Thornton Reference Thornton1998; Thornton Reference Thornton, Brown and Morgan2006; Lovejoy Reference Lovejoy2012; Reid Reference Reid2012; Stilwell Reference Stilwell2014). For example, from its formation in 1712 until its destruction at the hands of Muslim opponents in 1861, Segu (also known as Segou) depended on its slave army not just for security but also for its reproduction as a slave-raiding state (Bazin Reference Bazin1974; Roberts Reference Roberts1987; Klein Reference Klein1998; MacDonald and Camara Reference MacDonald, Camara, Monroe and Ogundiran2020). Dedicated slave soldiers were led by slave chiefs loosely in the service of the king. The king retained a separate retinue of personal armed slaves to act as political police in checking the loyalty of his subordinates (Bazin Reference Bazin1974, 134), once again underlining the extent to which the power of the central ruler depended on armed captives who had had their previous social ties violently severed. The slave soldiers lived off loot and replenished their numbers through forcible conscription of those male captives they did not kill or exchange for guns or other trade goods.

SLAVES UNDER THE STATE

The second mode of slave-based state-building might be more familiar: a polity based on a slave economy. Most infamously, slaves from Africa provided the workforce of the New World plantations of the antebellum U.S. South, the European Caribbean colonies, much of Spanish America, and Brazil. This corresponds with what Finley referred to as “slave societies” (Finley Reference Finley1980). Following Marx, others have referred to a “slave mode of production” (Sheriff Reference Sheriff1987, 2; Ejiogu Reference Ejiogu2011, 606; Quirk and Richardson Reference Quirk, Richardson, Suzuki, Zhang and Quirk2014, 450). In such societies, “slavery played a fundamental economic role in terms of how the elite derived its surplus; consequently, slavery also shaped the social, political and cultural aspects of those societies” (Vlassopoulos Reference Vlassopoulos2016, 6). State power deployed to maintain and reproduce slavery was the primary motor of the economy much more than market forces (Austin Reference Austin2008, 609). Lovejoy notes that such polities depended on an institutionalized basis for regular enslavement and an external slave trade (Lovejoy Reference Lovejoy2012, 11, 269). There was little meaningful separation between the state and the economy because the state enforced the system whereby people could be owned as property. The fundamental relationship is described by Scott with reference to slavery in Southeast Asia: “there was no state without concentrated manpower; there was no concentration of manpower without slavery hence all such states… were slaving states” (Scott Reference Scott2009, 85).

Thus, in these polities, there was a reciprocal political-economic dynamic whereby economic production was organized primarily by state power rather than supply and demand, while state power was itself dependent on the slave economy for its reproduction. In much of Africa but also much of Southeast Asia, the idea of relying on coercion to mobilize labor rather than the market was a long-standing practice, thanks to an environment where labor was scarce relative to land, and where populations were mobile (Reid Reference Reid and Reid1983; Reference Reid and Allen2022; Austin Reference Austin2008; Scott Reference Scott2009; Ward Reference Ward, Eltis and Engerman2011; Herbst Reference Herbst2014). Aside from slavery, such societies also had widespread dependence on other forms of forced labor, from debt bondage, to corvée, to pawnship. Reflecting the legacies of both Marxist and abolitionist thought on the subject, current liberal sensibilities suggest that slave economies were backward and stagnant; in fact, they often proved to be highly successful and dynamic (Thornton Reference Thornton1998, 91; Austin Reference Austin2008; Reid Reference Reid and Allen2022, 45).

This model of slave societies, what we refer to as “slaves under the state,” has been said to rely on “the usual Athens-to-Alabama narrative” that has dominated scholarship on slavery (Miller Reference Miller and Miller2009, 73), skipping from the ancient Mediterranean to the Americas. In contrast, we take a wider perspective. In line with the earlier criticism of the restrictive focus on the Americas and the Atlantic world in writing about slavery, this section first considers two examples from nineteenth-century West and East Africa, before making a brief reference to Southeast Asia. In Africa in particular, state-building efforts were crucially shaped by the effects of nineteenth-century European geopolitical and economic expansion, in two respects: first (counter-intuitively) the abolition of the trans-Atlantic slave trade, second the burgeoning demand from Western industrializing societies for primary goods from Africa. The combined effect was to foster reciprocal growth of the local slave economy and the power of the state apparatus.

With terrible irony, the growing effectiveness of the British-led ban on the trans-Atlantic slave trade in the first half of the nineteenth century both reduced the price of African slaves for African buyers and redirected the long-distance slave trade East to the Indian Ocean (Austin Reference Austin, Eltis, Engerman, Drescher and Richardson2017, 179; Ware Reference Ware, Eltis, Engerman, Drescher and Richardson2017, 344). At the same time, industrialization in Europe and North America reduced the price of manufactured goods, while substantially increasing the demand and hence prices for raw materials and agricultural goods from Africa (Laitin Reference Laitin1982, 712; Sheriff Reference Sheriff1987, 246; Bhacker Reference Bhacker1994, xxix; Northrup Reference Northrup2014, 192). Thus, although the nineteenth century is regarded as one in which Europeans came to dominate Africa, for most of the century the terms of international trade increasingly favored African producers.

These factors functioned as a massive stimulus for slave-based production in Africa. This was reflected in developments like the huge increase in slave cotton plantations along the Nile in the 1860s to make up for the disruption of the U.S. Civil War (Ware Reference Ware, Eltis, Engerman, Drescher and Richardson2017, 346), and the equally significant increase in slave-based palm oil, cocoa, and peanut production in West Africa (Laitin Reference Laitin1982, 688; Austin Reference Austin, Eltis, Engerman, Drescher and Richardson2017, 185). The increased revenues crucially bolstered domestic state-building efforts, and contributed to what has been referred to as “the African partition of Africa” that immediately preceded and was overtaken by the European carve-up of the continent from the 1880s, as slave-based African states consolidated and expanded (Herbst Reference Herbst2014, 50).

The largest and most powerful of these new slave-based nineteenth-century polities in West Africa was the Sokoto Caliphate. After the end of the trans-Atlantic slave trade, Sokoto built an economy that was heavily dependent on slaves, who came to make up a third or more of the total population (Lovejoy Reference Lovejoy2012, 195; Stilwell Reference Stilwell2014, 142; Austin Reference Austin, Eltis, Engerman, Drescher and Richardson2017, 183). There were entire villages populated by slaves and slave supervisors devoted to either growing food or producing cotton (Lovejoy Reference Lovejoy2016). The local development of the slave economy across the region was such that “[b]y the middle of the nineteenth century there were more slaves in Muslim areas of West Africa than in all parts of the Americas at any time in the history of the black Atlantic” (Lovejoy Reference Lovejoy2016, 160; see also Lovejoy Reference Lovejoy2012, xxiv; Klein Reference Klein1998, 1). Other non-Muslim African polities like Dahomey negotiated the transition from taking slaves for export to later using slaves for the production of primary goods as part of a “cash-crop revolution” that was once again driven by growing Western demand (Ejiogu Reference Ejiogu2011, 608; Lovejoy Reference Lovejoy2012, 161; Monroe Reference Monroe, Monroe and Ogundiran2020, 211). Slaves often became not just the main source of labor but also the most important stock of property and capital (Thornton Reference Thornton1998, 74; Herbst Reference Herbst2014, 38). This transition often had starkly gendered consequences: roughly two-thirds of the slaves taken across the Atlantic were male, whereas African slave-owners (and those in most other regions) generally preferred females (Klein Reference Klein2016, 332; Miller Reference Miller and Miller2009, 219). This gender preference often resulted in the killing of “excess” adult male captives (Klein Reference Klein1998, 4, 51; Campbell and Stanziani Reference Campbell, Stanziani, Eltis, Engerman, Drescher and Richardson2017, 229).

Turning to East Africa, the importance of this same relationship between the slave economy and state-building was readily apparent (Alpers Reference Alpers1975; Sheriff Reference Sheriff1987). Following centuries of migration and trade, the Omani Sultans’ sphere of influence ran along the Indian Ocean Swahili coast from current-day Somalia to Mozambique. With the decline of American markets for slaves at the turn of the nineteenth century, like their counterparts in West Africa, Omani elites headquartered in the East African island of Zanzibar reoriented from trading slaves to the production of primary goods using slave labor (Sheriff Reference Sheriff1987, 35; Ware Reference Ware, Eltis, Engerman, Drescher and Richardson2017, 362–3). From the 1820s in Zanzibar and the neighboring islands, tens of thousands of slaves taken from the mainland labored to produce cloves (Lovejoy Reference Lovejoy2012, 223–5; Ware Reference Ware, Eltis, Engerman, Drescher and Richardson2017, 362–93), feeding a market that generated spectacular wealth before collapsing in the 1870s. Along the coast, slaves produced grain for local and foreign consumption (Austin Reference Austin2008, 610; Stilwell Reference Stilwell2014, 170). Further inland, Omani expeditions hunted both slaves and ivory, eventually reaching as far as the Congo River. As they controlled and taxed the commodities produced by the slaves, the Omani rulers gained massive increases in customs revenue (Bhacker Reference Bhacker1994, 76). As was the case in West Africa, these customs revenues constituted the fiscal foundation of the state.

Turning to Southeast Asia, for rulers, nobles but also many religious leaders in charge of temples, “control of men, not land or capital, was both the key and the index to power” (Reid Reference Reid and Reid1983, 158; see also Ward Reference Ward, Eltis and Engerman2011, 170); this control was most apparent in slavery. The economic function of slaves was most pronounced in states like Siam, Laos, and Burma, where in the nineteenth century up to a quarter of the population were hereditary slaves (Mabbet Reference Mabbet and Reid1983, 57). For both fiscal and military reasons, state power depended on concentrated populations (Scott Reference Scott2009, 67–9). To this end, rather than market forces, it was massive forcible population transfers in wars against neighboring states, and endemic raiding against hill tribes, that replenished and sustained the necessary supply of slave labor (Ward Reference Ward, Eltis and Engerman2011, 174). According to Scott, “the taking of captives was the public purpose of statecraft,” with the effect that “whole regions were largely stripped of their inhabitants” (Scott Reference Scott2009, 87). In Southeast Asia, as in Africa, slaves were concentrated around the capital (Stilwell Reference Stilwell2014, 133). Scholars have repeatedly noted similarities in the nature and operation of Southeast Asian and African slavery (Reid Reference Reid and Reid1983; Scott Reference Scott2009, 72–3; Klein Reference Klein2016, 327). This observation strongly indicates that the model of “slaves under the state” has relevance, and legacies, far beyond the Atlantic world.

SLAVERY AND INTERNATIONAL ORDERS

If the first main theoretical contention of this paper is that the institution of slavery was often fundamental in state-building, the second is that slavery was often crucial in the construction and operation of international networks, and perhaps international orders, as relations became routinized with increasingly shared norms.

Slavery was global not just in the sense that it existed in many different societies all over the world. More importantly, it was global in the deeper sense that different polities were often tied together through the patterns of violence and exchange that underpinned slavery. These links were more and more important in the modern era, as slaving orders increasingly extended across continents and oceans in line with the expansion of empires and the globalization of the world economy. These international slaving orders shaped and were shaped by norms, war, and trade. Our coverage in this section is very different from historians’ ideas of “global” or “world” history as studies of slavery in a single non-European polity. We escape from “the tyranny of the particular” (Allen Reference Allen2022, 2) via a comparative and connected treatment of slavery from the perspective of international slaving orders (Klein Reference Klein2016, 331; Vlassopoulos Reference Vlassopoulos2016, 20; Austin Reference Austin, Eltis, Engerman, Drescher and Richardson2017, 194).

Slavery had particular features that brought polities into sustained relations with each other, and thus is particularly important for International Relations, a linkage that has so far been conspicuously overlooked (Pella Reference Pella2015, 149). This international aspect reflected the fact that, first, groups as distant as pre-Columbian Amerindians, Europeans, Persians, and many African societies shared a normative reluctance to enslave members of their own community (however defined). As such, the demand for slaves was often directed externally toward other groups. Second, and relatedly, although slavery was sometimes the result of debt or judicial punishment, the most common route into slavery historically was through capture in war or raiding. Slaves were a by-product and at times the primary aim of organized violence (Scott Reference Scott2009; Herbst Reference Herbst2014, 43). Finally, as polities became increasingly dependent on slavery according to either of the two models presented above, they often outran their local supply of slaves, and thus had to turn to long-distance trade to cover the deficit. When this occurred, a symbiotic international relationship arose between specialized polities that produced slaves for export and those that imported them. The crucial point for International Relations scholars is that slavery simultaneously created or reinforced normative and identity boundaries between in- and out-groups, while often promoting extensive and durable military and commercial relations across such boundaries—relations which sometimes congealed into international orders.

The first example is the Ottoman Empire and its role in creating and sustaining an international slave order (the observations are also relevant to other similar Islamic polities discussed above). In line with Islamic precepts (Sheriff Reference Sheriff2018), the Ottomans were normatively prohibited from enslaving other Muslims. Though compliance with this principle was not absolute (depending on who was judged to be a Muslim), it was widespread. In the early stages of their empire, the Ottomans were able to meet their own needs for slaves through frontier raiding and campaigns of conquest, as described earlier. By the seventeenth century, however, the Ottomans had increasing difficulty in procuring slaves through conquest. The shortage was compounded as the manumission of slaves was common (though not obligatory), and slavery was often not hereditary. There was no debt slavery. Yet the demand for slaves remained high. In response, the empire became the center of an international slaving order whereby a variety of specialized slave-raiding polities supplied the Ottoman demand.

Many of the same elements were present in the much better known (or at least partially known) Atlantic international slaving order. Norms prevented the enslavement of Christian Europeans, originally on a religious, and increasingly on a racial basis. At first, Europeans met the demand for New World slaves by capturing local inhabitants. However, Europeans quickly ran short of victims, and the rise of the plantation economy massively increased the demand for labor (Klein Reference Klein1998, 3; Lovejoy Reference Lovejoy2012, 47; Pella Reference Pella2015, 80). Initially, Europeans had sought to forcibly enslave Africans, but their raids were quickly defeated by local opposition. Instead, Europeans moved to purchase slaves from African rulers and traders (Thornton Reference Thornton1998, 38, 125). This in turn gave rise to African slaving states whose primary function, like those polities “feeding” Ottoman demand, was the militarized production of slaves for export (Klein Reference Klein1998).

Despite radical differences in the domestic nature of slavery in these two different settings, there are important parallels and commonalities between the Ottoman and Atlantic international slave orders. In both contexts, deep normative commitments defined the set of those who could be enslaved to religious or racial outsiders. Within these normative limits, enslavement was allowed mainly as a result of war and conquest. Yet, thanks to military obstacles and recurrent demand for new slaves, the Ottomans and Europeans ran up against limits in meeting their demand for slaves themselves via military means. As a result, both had to rely on an increasingly long-distance trade with polities that specialized in capturing and exporting slaves. A final commonality was that both international slave orders were undone by the exercise of European (mainly British) extraterritorial imperialism, at first in the Atlantic from the early 1800s, and then in the East toward the end of the century.

INTERNATIONAL SLAVING ORDERS: THE OTTOMANS

From as far back as the eighth century until the rise of the trans-Atlantic trade, the international slave trade was driven primarily by demand from the Islamic world. The Zanj slaves taken from East Africa to current-day Iraq provide an early example in the eighth and ninth centuries (Sheriff Reference Sheriff2018). From the tenth century onward, the Vikings increasingly sold the people they captured in their raids to Muslim markets (Heeboll-Holm Reference Heeboll-Holm2020, 440). Why did many Islamic polities constantly need to import slaves? In slaving polities ruled at least partly according to Islamic norms, demand was continuous, because converts to Islam were often manumitted, and slave status was only sometimes passed down across generations (Toledano Reference Toledano, Eltis and Engerman2011, 29; Sheriff Reference Sheriff2018, 250). The religious regulation of slavery in Muslim societies thus kept the demand for new slaves high until at least the late nineteenth century (Toledano Reference Toledano, Eltis and Engerman2011, 30). This demand created both slave raiders and trade networks of slavery, which then evolved into more complex orders. To this extent, the development of the Ottoman system of slavery followed the experience of the Abbasid Caliphate and the Zanj slaves almost a thousand years before (Sheriff Reference Sheriff2018, 250).

Initially, the two most important polities whose political economy depended on the capture and sale of slaves to the Ottomans were the Crimean Tatars and the Barbary corsairs. The Crimean Khanate was a post-Mongol Ottoman vassal state in the Northern Black Sea steppe. They raided extensively across present-day Russia, Ukraine, Belarus, Poland, and the Caucasus. The Tatars referred to their slaving as “harvesting the steppe,” with the slaves themselves referred to as “speaking property” (Kizilov Reference Kizilov2005, 975). The slave trade is described as “the backbone of the Crimean khanate’s economy” (Brown Reference Brown2015, 346). Although Christian slaves were sometimes used as local agricultural labor, most were sold to the Ottomans. Captives were first shipped across the Black Sea to Istanbul, where many were then sold again further afield, with some ending up in North Africa, Persia, or occasionally even Western Europe (Kizilov Reference Kizilov2005, 966). Klein puts the number of slaves captured and sold by the Crimean Tatars at 2.5 million 1450-1700 (Klein Reference Klein2016, 337).

The Barbary corsairs were mostly Ottoman tributary polities, pledging their suzerainty to the Sultan from the early 1500s, but in practice self-governing from their bases in Algiers, Tunis, Tripoli, and elsewhere along the North African coast. The basis of the corsairs’ political economy was the export of slaves. The corsairs pursued their maritime slaving-raiding in the Mediterranean, but also along the coast of Southern Europe, and sometimes in Atlantic Europe as well. They are estimated to have captured around 1.25 million predominantly European slaves in the period 1530-1780 (Agoston Reference Agoston2021, 112). These were sold mainly to the Ottoman Empire proper, but also elsewhere in the Islamic world (Lowenheim Reference Lowenheim2003). However, the corsairs also retained significant numbers of slaves to man their galleys, and perform labor on public works, in agriculture, and in the household. Note that while we refer to both the Crimean Khanate and the Barbary corsairs as tributaries or vassals of the Ottomans, the relationship was one of mutual dependence, more reminiscent of international networks, regimes, alliances, or even orders of the present day.

The final evolution of this international slaving order was the progressive shift of the slave supply away from Europe and Europeans toward Africa (Ware Reference Ware, Eltis and Engerman2011, 51; Ferguson and Toledano Reference Ferguson, Toledano, Eltis, Engerman, Drescher and Richardson2017, 198; the Caucasus remained a partial exception). The Crimean Tatars were contained and then defeated by the Russians in the 1700s, while the corsairs were militarily suppressed in the early nineteenth century at the hands of several European powers and the United States (Lowenheim Reference Lowenheim2003). Centers like Algiers then became entrepots, as slaves were taken from the interior of West Africa and marched across the Sahara to the Mediterranean Coast. Of those who survived, some were kept for local use in North Africa, but most were sold on to Ottoman owners (Lovejoy Reference Lovejoy2016, 156–7). This trans-Saharan slave route to the Ottoman Empire endured until the early twentieth century (Austin Reference Austin, Eltis, Engerman, Drescher and Richardson2017). In East Africa, the Ottomans sourced slaves from present-day Sudan, as well as from Ethiopia via the Red Sea (Ware Reference Ware, Eltis and Engerman2011, 69, 71). The Ottoman slave trade peaked in the nineteenth century (Ferguson and Toledano Reference Ferguson, Toledano, Eltis, Engerman, Drescher and Richardson2017, 199), when in total something like 1.3 million African slaves were brought into the empire (Toledano Reference Toledano, Eltis and Engerman2011, 26). In both the West and the East African trade to the Islamic world, slaves were mostly female, mainly intended to join households, with some eunuchs, who attracted the highest prices (Lovejoy Reference Lovejoy2012, 5). Even after the end of the janissaries, the use of slave soldiers continued into the nineteenth century on a reduced scale, with Ottoman-Egyptian slave soldiers being used to expand Ottoman Africa (Lovejoy Reference Lovejoy2012, 150; Stilwell Reference Stilwell2014, 105).

Many of the same observations hold for other Islamic polities. For example, Persia and the polities of the Persian Gulf not only operated under the same religious precepts as the Ottomans but also saw the same evolution whereby earlier on slavery was most significant in terms of male slaves used as administrators and soldiers, while later there was a shift to female slaves for the household. Racially, there was a similar trend away from European slaves toward Africans, though European slaves continued to be the most expensive (Ware Reference Ware, Eltis, Engerman, Drescher and Richardson2017, 365). So too there was a move from obtaining slaves by direct predation and raiding, toward joining a far-flung international slave order whereby slaves were taken from distant sources by specialized slaving polities, and then transported by a series of relay trades to their final destination. For example, after the Persian defeat in their last war with the Russians in 1828, the Persians lost most of their access to slaves from the Caucasus, causing the substitution of more African slaves instead (Ware Reference Ware, Eltis, Engerman, Drescher and Richardson2017). The slave trade from Northeast Africa to the Islamic world continued well into the twentieth century, with Persian Gulf states importing some African slaves even after World War II (Campbell and Stanziani Reference Campbell, Stanziani, Eltis, Engerman, Drescher and Richardson2017, 233).

The main point here is that it is impossible to understand how the institution of slavery worked in the Ottoman Empire or the Islamic World more generally without seeing it as part of a sprawling international order. Though it changed over the centuries, Ottoman slavery was always inherently international. At first this was in terms of wars of expansion and conquest, then later in terms of long-distance trade supplied by the development of specialized exporter slaving states, some on the fringes of the empire, some well beyond it.

INTERNATIONAL SLAVE ORDERS: THE ATLANTIC

The Atlantic international slaving order is deceptively familiar. As noted, scholarship on slavery in the modern era is overwhelmingly focused on the importation of African slaves to the Americas. Yet the coverage has been partial and biased in crucial aspects. First, to the extent this is written about as a system, coverage is commonly only in economic terms, especially the triangular trade of slaves and plantation goods between Africa, the Americas, and Europe, but very rarely as an international political order (Bennett Reference Bennett2019, 134). Second, given the usual focus on Americans and Europeans, there is much less attention paid to Africa and the agency of Africans (Laitin Reference Laitin1982; Thornton Reference Thornton1998; Herbst Reference Herbst2014; Northrup Reference Northrup2014). In response, this section concentrates on the political nature of the Atlantic international order, and foregrounds the essential role played by (some) Africans as autonomous actors in that order.

As noted previously, after the Middle Ages, reigning religious norms prohibited Europeans from enslaving other Europeans, particularly Christians (Eltis and Engerman Reference Eltis, Engerman, Eltis and Engerman2011, 18; Vlassopoulos Reference Vlassopoulos2016, 26). As such, Europeans’ demand for slaves was turned outward through war and imperial expansion. The main demand for slaves came with European expansion in the Americas (though Europeans also used slaves in the East, for example the Spice Islands of present-day Indonesia, Reid Reference Reid and Reid1983, 23, 34). At first, this demand was met in the Caribbean islands and the American mainland through the use of captured locals in agriculture and mines. Yet horrifically high death rates resulting from a combination of European violence, harsh working conditions, and newly introduced diseases meant that the supply of slaves struggled to keep up with demand (Snyder Reference Snyder2012, 65; Inikori Reference Inikori, Akyeampong, Bates, Nunn and Robinson2014, 72). The response was increasingly to bring slaves across the Atlantic from West Africa.

From their earliest contacts in the mid-1400s, the Europeans incrementally advancing along the Atlantic Coast of Africa had sought slaves (Thornton Reference Thornton1998; Bennett Reference Bennett2019). By the 1500s, the Portuguese had begun to establish sugar plantations on African islands such as Sao Tome. This model was later transported to Brazil and elsewhere in the Americas, leading to an explosion in the production of crops like sugar, tobacco, and cotton. Accordingly, from the mid-1600s, there was a corresponding spike in the demand for plantation slave labor (Inikori Reference Inikori, Akyeampong, Bates, Nunn and Robinson2014, 79). Yet from the outset, European attempts at taking African slaves by force had generally met with failure, thanks to local opposition (Thornton Reference Thornton1998, 37–9; Northrup Reference Northrup2014; Bennett Reference Bennett2019). Any advantages Europeans had in their ocean-going ships and gunpowder weapons were not sufficient to overcome African military resistance.

Thus Europeans faced two different fundamental limitations on their access to slaves: normative prohibitions that prevented enslaving Europeans, and military incapacity that prevented them from taking Africans via war. The Atlantic slave trade was crucially shaped by these two considerations; the fact that it was a trade at all, rather than some other kind of interaction, was because of these normative and military limitations, and yet neither factor receives attention in the traditional economic treatment of the subject. Nevertheless, it is impossible to understand the trans-Atlantic slave trade without considering the broader political factors within which it was embedded.

As a result, Europeans quickly defaulted to a system that lasted for over 300 years, until the abolition of the Atlantic slave trade in the nineteenth century. Traditional treatments of the Middle Passage tend to start at the water’s edge, where Europeans took control of their victims. Yet this ignores the crucial question of how these slaves were obtained in the first place. Slaves were supplied by African merchants and rulers, who generally drove a hard bargain in selling to the Europeans (Northrup Reference Northrup2014, 55). As the demand for slaves rose with the expansion of the New World plantation economy, the price of African slaves rose by a factor of four or five (Law Reference Law1994, 58; Lovejoy Reference Lovejoy2012, 51). In obtaining African slaves, European slavers had to operate according to African rules (Thornton Reference Thornton1998, 7, 74; Pella Reference Pella2015, 83; Bennett Reference Bennett2019, 68).

Over the centuries and across the continent, there was a huge variety of arrangements for supplying slaves, but there were also important common patterns. Just as a multiplicity of actors and a complex skein of relationships constituted the slave-based oceanic triangular trade, the same situation obtained in the African interior also. In some cases, the same African rulers that supplied the Europeans with slaves captured them through war and raiding, whether it was the Kongo Kingdom in the 1500s (Heywood Reference Heywood2009), or Dahomey centuries later. Elsewhere, however, Africans on the coast in direct contact with Europeans were intermediaries, the coastal terminus of inland relay trades through which slaves were repeatedly bought and on-sold. In many such cases, the ultimate source of supply was African slaving states that, somewhat akin to the Crimean Tatars and Barbary corsairs that fed the Ottoman slave market, were institutionally oriented to the militarized production of slaves for foreign markets (Roberts Reference Roberts1987; Klein Reference Klein1998; Robinson Reference Robinson2002; Stilwell Reference Stilwell2014; Green Reference Green2020).

A final point relates to the links between these two international slaving orders. As the Ottoman and Islamic world more generally came to take its slaves from Africa for reasons discussed above, some African providers (many themselves Muslim, though not all) served both Atlantic and Islamic markets simultaneously. Polities like Segu around present-day Mali sent some of their slaves West to the Senegambian Atlantic Coast, from where they were shipped to the Americas, while others were taken across the Sahara and then to the Middle East (Roberts Reference Roberts1987). Ultimately, British hegemony undermined both systems, with pressure on first West African polities to discontinue the trade, and then later on the Ottomans, Omanis, and Persian Gulf emirates.