Which of the following would most strongly support Carter's contention in his phrase "we were taught that our enemies were always invincible"?

The choice that most strongly supports Carter's contention in his phrase "we were taught that our enemies were always invincible" is the defeat of South Vietnam by North Vietnam in 1975. This event exemplifies how the United States and its allies regarded the communist forces as formidable adversaries, capable of achieving significant military victories despite American intervention and support for the South Vietnamese government. The fall of Saigon marked a dramatic conclusion to a prolonged conflict where the U.S. had believed that it could prevent communist expansion in Southeast Asia. This outcome would reinforce the belief that enemies, particularly those perceived as ideologically driven, could be far more resilient and successful than anticipated, aligning closely with Carter's assertion about the invincibility of perceived adversaries.

While the other choices also address significant issues of the time, they do not encapsulate the specific notion of an invincible enemy as directly as the outcome of the Vietnam War. The rise of communism in Eastern Europe reflects more on the spread of ideology rather than military defeat. Economic challenges in the U.S. pertain to domestic issues rather than perceptions of enemy strength, and the success of the Persian Gulf War demonstrates a situation where the U.S. forcefully overcame its enemies, contrasting with the idea of