Ironically, the American love affair with the UN would mask some real changes to the organization. Not only did the Cold War make the federalists irrelevant, it stripped the Security Council of authority at the very moment that it most needed support. With the Soviet Union increasingly using its permanent veto to block enforcement action by the UN's American-led majority, the UN could not live up to its promise. Only in Korea during 1950, and then solely because a Soviet boycott of the Security Council left the USSR unable to exercise its veto, did the UN come close to addressing its original purpose. As a rule, the veto shifted the UN to the periphery of world politics. Americans increasingly came to associate collective security not with the UN but with the North Atlantic Treaty Organization, formed in 1949. But NATO was much closer to being a traditional military alliance than a universal collective security organization. As long as the UN would be hampered by the Soviet veto—which meant that so long as the UN would not serve as a convenient instrument of American foreign policy—Cold War internationalists like Dean Acheson, secretary of state from 1949 to 1953, would hold it in disdain.
The Great Depression, World War II, nuclear weapons, and the Cold War had discredited isolationism. But internationalists may have celebrated their victory too casually. If nearly everyone had become an internationalist, then the term was in danger of losing its meaning, which is exactly what happened during the next forty years. Indeed, many outspoken nationalists proclaimed themselves internationalists, promoting the projection of U.S. power throughout the world through the new system of alliances. Yes, they admitted, the world had shrunk. Economic interdependence and advances in communications and weaponry—including intercontinental bombers and missiles—made cooperation expedient. But it was anticommunism, not technology, that served as the glue holding their foreign policy worldview together, and anticommunism, as the McCarthy era proved, was often associated with xenophobia and unilateralism.