Chapter 5 examines exchanges of material cultures. Through the paradigm of ‘domestication’, it shows how lakeshore populations incorporated several commodities circulating the wider Indian Ocean World into their everyday lives, while also showing how coastal traders sought to affect the supply of these objects to enrich their commercial networks. The principal items discussed are glass beads, cotton cloths, and guns. The chapter uses the Lake Tanganyika case study to show how demand for specific products in East Africa affected broader commercial patterns that traversed the wider Indian Ocean World, which themselves were concurrently being affected by the spread of capitalism from Europe. Additionally, it shows how patterns of consumption on the lakeshore served to enhance the status of several bonds(wo)men, suggesting a contravention of often assumed links between being in bondage and of having low social status.

Chapter 3 uses archival and anthropological sources to examine human encounters with Lake Tanganyika itself. The lake was a source of food, a barrier to cross, and the subject of religious and political innovation. How these features of human–lake encounters were understood shifted over time in ways that were related to the exchange of cultures and fluctuations in the lake’s level. In general terms, these shifts can be summed up as the ‘commercialisation’ of encounters with the lake, which affected how people crossed it, their motivations for doing so, and their means of appeasing spirits they believed to inhabit it. Technology, environmental factors, and religious paradigms with links to the wider Indian Ocean World affected how people crossed, used, and interpreted conditions on the lake.

The book finishes with an epilogue that shows how examining encounters in the deep interior helps to further contextualise one of the most well-known episodes in coastal East Africa’s nineteenth-century history, namely the urban riots of 1888 and the subsequent outbreak of the Abushiri Rebellion (1888–90). Far from being an unimportant periphery, Lake Tanganyika was key a frontier zone of the Indian Ocean World during the nineteenth century, the conditions in which affected the broader trajectory the wider Indian Ocean World’s history, especially the history of the East African coast.

Chapter 7 examines the history Islam on Lake Tanganyika’s shores. It explores the ways in which coastal traders adapted their religious practices to the lakeshore environment, and how new converts adapted their new religion to their pre-existing knowledge of the spiritual world. In line with recent Indian Ocean World historiography, it uses a ‘bottom-up’ approach to conversion, contesting trends in older Africanist works that focused on the conversion of elites. In this case study, this means an examination of bonds(wo)men’s importance to the spread of Islam, who, through claiming ‘freeborn’ social status, also claimed the right to convert. This allows for a greater appreciation of Islam’s influence on the lakeshore, to the extent that the lake becomes understood as an ‘Islamic Sea’ – similar in conception to the Indian Ocean over the longue durée.

Chapter 6 analyses systems of bondage on the lakeshore. It builds on recent works in Indian Ocean World history that have blurred the distinctions between slavery and freedom, and challenges trends in Africanist scholarship that have tended to analyse labour and social relations in these terms. It argues that the terms ‘slavery’ and ‘freedom’ do not do justice to the wide variety of bonded forms that existed on Lake Tanganyika’s shores. Most labourers living on the lakeshore were not concerned with the distinction of being either a ‘slave’ or ‘free’. Rather, they were concerned with who they were bonded to, the conditions of their bondage, and what this meant for their social status. In this instance (and perhaps paradoxically), some bonds(wo)men were able to claim ‘freeborn’ social status. They demonstrated this status through their display of material objects, their primary occupation, and their spiritual capabilities.

Chapter 4 examines relationships within coastal trader communities, focusing on Omani and Swahili populations. It traces the existence of factions whose roots lay in historical developments on the coast, and then sheds light on power shifts between them across coastal and inland regions. It argues that despite there being a ‘pioneer ethic’ that in some ways bound coastal traders, there was always an ‘undercurrent’ of competition and conflict, which became more robust as the period went on. Unlike at the coast, on the shores of Lake Tanganyika, this ‘undercurrent’ was often manifested in violence. This was a symptom of the recency of coastal traders’ arrival in the region, a lack of formal institutions from the coast that followed them inland, and the highly competitive nature of ivory trading. Violence between coastal traders on the shores of Lake Tanganyika was the surface manifestation of deeper tectonics whose roots lay in the Indian Ocean World’s littoral core.

Chapter 2 examines an ‘agricultural revolution’ in the rural areas around Lake Tanganyika’s emporia, characterised by changes in labour regime, crop choice, and land-use. It uses climatological sources and the wider context of the Indian Ocean monsoon system to examine how the introduction of new crops (cassava, maize, and rice) affected agricultural productivity and vulnerability to the effects erratic climatic conditions, including droughts and floods. It argues that benign environmental conditions in the Indian Ocean World during mid-century contributed to the viability of large port-towns. However, erratic rainfall from 1876 onwards, the replacement of East African staples with less drought-resistant crops, and the increased demands on the region’s agricultural supplies from emporia and the caravan trade exacerbated trends towards violence and instability during the late 1870s and 1880s.

Chapter 1 explores the emergence of port-towns on Lake Tanganyika’s shores. It uses archival and archaeological sources to situate this history within the broader contexts of ‘emporia’ in the Indian Ocean World over the longue durée, but with particular reference to transitions that occurred in the nineteenth century. Despite being adapted to their own micro-environments and peoples, the organisation and architecture of Lake Tanganyika’s nineteenth-century port-towns owed much to patterns that transcended parts of the wider Indian Ocean World. Such patterns are observable in terms of architecture, layout, and engagement with the water-facing environment.

This introductory chapter explores links between Lake Tanganyika, East Africa, and the wider Indian Ocean World in history and historiography. It does so firstly by stressing the peculiarities of Lake Tanganyika’s shape and environment in the East African context. It then draws on a wider historiography of lakes and oceans in world history, and it argues that doing so necessitates taking on perspectives from the wider Indian Ocean World. But, far from being a place where patterns from the wider Indian Ocean World replicated themselves, Lake Tanganyika was a ‘frontier’ where phenomena traditionally associated with the macro-region (including e.g. Islam, boating technologies, and fashions) were negotiated and reimagined in particularly robust ways. This applies especially to the period c.1830–90, during which coastal and Great Lakes populations encountered each other in significant numbers for the first time, caused by the expansion of the global ivory trade.