This article builds on the intellectual legacy of Jan Tinbergen by extending his analysis on welfare and security into a framework involving strategic interaction. I first incorporate welfare and security in terms of interstate tensions into a single utility or payoff function. An uncertain world is characterized by states that are more peaceful, and others where nations are more hostile to each other. Both conflictual and peaceful outcomes lie along a spectrum of hostility short of war. The strategies adopted by the two countries, which promote peace, can be complements or substitutes. This means that they can go up or down in response to increases in the strategies of its rival. I demonstrate that noncooperative behaviour between nations is Pareto inferior to cooperative behaviour, because the latter is associated with more actions and efforts to promote peace. Cooperative behaviour is akin to Tinbergen’s notion of world government. Non-cooperative behaviour by states also leads to moral hazard, and there can be free-riding in joint peaceful behaviour by some nations, particularly when the strategies of the countries are substitutes. The model is extended to aggressive international behaviour, including that mandated by populist plebiscites or election victories, as well as an outline of individual behaviour driven by identity-based politics.