1940s: World War II was a decisive victory for the United States and its allies and was widely supported by Americans. Americans' knowl­edge of the war came from delayed accounts in newspapers, on radio, and in newsreels shown in movie theaters. By the end of the war, the United States was the top military and economic power in the world.

1960s: American involvement in the Vietnam War eventually lost the support of most citizens, perhaps in part because of extensive television news coverage, which brought the realities of war into American living rooms. The war con­cluded in 1975 with the United States with­drawing from Vietnam-the only war America ever lost. While still the "leader of the free world," the Vietnam War deals a strong blow to American prestige around the world.

Today: The United States's most recent mili­...