This study recounts the history and practical politics of creating a world in which the rule of law maintains the peace in the same way as in well-organized free national states. The coming of the Cold War by 1947 is the principal explanation for the immediate failure of the world federalists. The historic opportunity for so fundamental an innovation in international relations as the establishment of even a limited world federation had passed, but for the next few years there was a vigorous and deep political thinking about the continued prospect of war. Work toward this goal continued, and eventually the United World Federalists built up enough of a popular movement to pass resolutions favoring U.S. participation in twenty-two states.