Bangladesh, Sept. 23 -- For decades, the United Nations General Assembly has served as one of the world's most visible stages for diplomacy. Every year, presidents, prime ministers and political leaders gather in New York to present their countries' positions, appeal to international opinion and reaffirm the principles of the international system. Yet the political atmosphere surrounding the General Assembly has changed considerably. The speeches remain, but the belief that they can by themselves alter the course of major conflicts appears increasingly fragile.

The General Assembly once provided a dramatic stage for the great ideological confrontations of the twentieth century. The Cold War turned the UN chamber into a forum where the r...