Keohane argued that international cooperation can persist even after the decline of a dominant hegemonic power. Accepting realism's assumption that states are rational egoists, he showed that self-interest can lead to cooperation through international regimes—institutions and norms that reduce transaction costs, provide information, and facilitate decentralized coordination among states.[reference:0] The persistence of cooperation after U.S. hegemony waned in the 1970s proved, for Keohane, that hegemony is not a necessary condition for order.

Both accept that states are rational, self-interested actors operating in anarchy. But where neorealists like Kenneth Waltz predict inevitable conflict and distrust, Keohane argued that institutions can mitigate anarchy's worst effects by lowering transaction costs, creating focal points, and enabling reciprocity.[reference:1][reference:2] Neorealists see relative gains as paramount; Keohane contended that states often pursue absolute gains through cooperation, especially in economic and environmental domains.

Introduced with Joseph Nye in *Power and Interdependence* (1977), complex interdependence describes a world where multiple channels connect societies, military force plays a diminished role, and no single hierarchy of issues exists.[reference:3] It challenged realism's assumption that security and military power dominate all international interactions, establishing international political economy as a distinct subfield and paving the way for institutionalist theories of cooperation.[reference:4]

The World Trade Organization, International Monetary Fund, and Paris Agreement on climate change are all international regimes of the kind Keohane analyzed. More recently, he examined 'regime complexes'—overlapping, non-hierarchical institutions like those governing climate, trade, and finance—that manage global problems without central authority.[reference:5] His work also informs the design of accountability mechanisms for global governance institutions.[reference:6]

Many assume Keohane is a utopian idealist who believes states naturally cooperate. In fact, he explicitly accepts realism's assumptions about rational self-interest and anarchy.[reference:7] His contribution is showing that cooperation can emerge *from* self-interest, not despite it—a rigorously rationalist, not idealist, argument. He also does not claim institutions eliminate power; rather, they shape how power is exercised.[reference:8]

His framework for understanding how institutions enable cooperation under anarchy has been adopted in comparative politics, organizational theory, and law. *Designing Social Inquiry* (1994), co-authored with Gary King and Sidney Verba, became a methodological touchstone for qualitative research across political science.[reference:9] His concepts of accountability and legitimacy in global governance also inform debates in political philosophy and international law.[reference:10]