Nevertheless, the nation had indeed shifted decisively toward a more internationalist position. Washington quickly and quietly joined UN-related agencies like the new International Court of Justice (which replaced the older Permanent Court of International Justice) and the International Labor Organization. (The United States had actually joined that organization in 1935, but only because ILO proponents emphasized its separation from the League of Nations itself.) Membership in both came with some of the usual nationalist protections, such as the Connally Amendment preventing the International Court from hearing cases that Congress considered within the "domestic jurisdiction" of the United States.
Not all Americans accepted the United Nations unquestioningly. A vocal isolationist remnant, led by Senator Robert Taft, challenged the new internationalist faith and its emphasis on sanctions and entanglement. A small but visible group of internationalists, too, raised concerns about the UN. They complained not that the UN had too much power, but that it had too little. Where isolationists and nationalists feared that the new organization would compromise American sovereignty, the internationalist critics mainly argued that the UN left its members with too much sovereignty. Many called for a world federation, more or less inspired by Clarence Streit's Union Now (1939). UN proponents may have stolen much of Streit's thunder, but his movement continued to promote the federation ideal, which emphasized the primacy of people rather than states. This became evident in 1958, when Grenville Clark and Louis B. Sohn published the most famous treatise on the subject of federalism, World Peace Through World Law. They proposed that the UN General Assembly become the foundation of the new system, with delegates elected by subject populations and not selected by sovereign governments. Law, not national interest, would be the driving force behind the federation, therefore ensuring the likelihood of permanent peace.
Considered utopian by most academic writers, this brand of internationalism never achieved real popularity. A diverse coalition of groups called Americans United for World Organization sought to mobilize support for this kind of federalism even before the end of the war, but internal disputes eventually rendered it impotent. In 1947 it merged with a few other federalist groups to form its better-known successor, United World Federalists. This organization, too, failed to dent the pro-UN consensus. In part, its timing was wrong. Federalism necessitated international cooperation, exactly the opposite of what occurred after 1947 as the Cold War became the dominant international reality. Ideological differences and military alliances rendered the federalists irrelevant.