The modern international order faces profound challenges. Power is shifting to non-Western states and diffusing to non-state actors, including transnational insurgents. This is more than a power transition: it also about culture. Western states now share the stage with powers such as China who bring their own cultural values, practices, and histories, and new forms of transnational violence are justified in the name of religious identity and belief. Some see this as a fundamental threat to modern international order, an order created by and for the West. Others see the “liberal” order as uniquely able to accommodate states and peoples of diverse cultures. How well equipped is IR to contribute to these debates? I review four recent works on the future of the modern international order, asking what conceptual, theoretical, and empirical resources they offer for understanding the relationship between cultural diversity and international order. This literature suffers from four limitations: culture is essentialized or bracketed; institutions are seen as either simple expressions of cultural values or structures that neutralize culture, with their recognition function ignored; the structural power of international orders—how they produce political and cultural subjectivities—is underappreciated; and international orders are conceived too narrowly as orders of sovereign states. To overcome these limitations, I advance a new perspective on cultural diversity and international order. International orders evolve in heterogeneous cultural contexts, and the governance of diversity is a key imperative of order building. In response, international orders develop diversity regimes: institutional norms and practices that define legitimate units of political authority, authorize certain forms of cultural difference, and relate the two. These regimes are essential to the legitimacy of international orders, but face two interrelated pressures for change: shifts in underlying material capabilities, and new claims for cultural recognition, often rooted in grievances against past or prevailing forms of recognition.