On 20 December 1999, the Portuguese-administered territory of Macau formally reverted to Chinese rule. Macau's reincorporation into China passed with little fanfare outside East Asia, attracting far less global media scrutiny than the handover of Hong Kong two years previously. And yet it marked the end of a critically important era of world history, signifying the end of one of the last vestiges of the diversity of political arrangements that had attended Western expansion into Asia. While Beijing will govern Macau as a Special Administrative Region until 2049, the Macau transfer constituted a final pre-millennial instance of the sovereign state's universal triumph over empire, and with it the apparent vindication of scholars who anticipate that interaction promotes global convergence in polity forms.

Considering the first three centuries of large-scale Western participation in the Indian Ocean regional international system, we contest the view that interaction always promotes sameness between political communities. This chapter proceeds in four sections. We begin by examining conventional theories of the presumed nexus between interaction and homogenization. Focusing especially on realism, rationalism and closely related constructivist and sociological institutionalist accounts, we demonstrate that these approaches each predominantly rely on causal mechanisms whereby interaction produces a convergence on a common polity form via some combination of competition or conformity. The primary problem with such accounts is the historical prevalence of diverse international systems, but there are also conceptual weaknesses in each of these perspectives. In the second section, we briefly contrast these claims against a growing literature that establishes diversity, rather than uniformity, as the default condition of most international systems throughout history. Notwithstanding their predominant focus on explaining homogeneity and convergence, the third section shows that these major theoretical traditions do nevertheless contain implicit theories of diverse international systems. Diversity might reflect the difficulty of power projection, asymmetrical alliances, economic specialization, the contracting out of sovereign prerogatives between unequal powers, or stratification between diverse units under normative regimes of unequal entitlement.