In the law of peoples, Rawls argues that a world of liberal and decent peoples would be peaceful and stable for the “right” reasons (LP 44–54). He draws on the democratic peace thesis. This thesis holds that war is less likely to occur between two democracies than between either a democracy and a nondemocratic society or two nondemocratic societies. Another version of the thesis holds that democracies are simply more peaceful than nondemocratic societies. Rawls invokes this latter interpretation in his argument, though other interpretations may support his position too. (See Hayes 2011 and Ray 1998 for reviews of the democratic peace literature.)

The democratic peace thesis consists of a factual and a causal claim. The factual claim refers to the historical absence of war between democracies. Some trace this peace back to the early 1800s, while others hold that the post-World War II era is most signiicant, since few democracies existed before 1939.

The causal claim holds that some feature of democratic society causes the peace. There are several competing, and perhaps complementary, versions of the causal claim. One holds that shared values lead to trust between democracies. Another holds that constitutional restraints inhibit war. The economic interdependence view holds that war is unattractive because it interferes with trade and other economic relations. Reelection constraint accounts depend on democratic voting and the political consequences of unpopular wars.