Question 3: How did official US policy towards Vietnam change between 1950 and 1975? How did American leaders link events in Vietnam to national security interests? How did the American public react to the war in the sixties and early seventies?
Answer: These two questions are so intertwined with one another that combining the two answers is the most efficient way of telling the story. Vietnam was a legacy of Kennedy and a primary reason for the split in American society.
I think one of the biggest reasons for such a change in American's ideas and confidence comes from a major generational gap. The difference between the WWII era citizens ("the greatest generation") and their children ("baby boomers") is dramatic and holds within itself some of the keys to the answer. The answer also lies within sociological and political changes that occurred in and around the 60's.
During WWII, America had devoted itself almost entirely to the war effort. Countless numbers of able-bodied men were in the service in the Pacific and European theaters. Millions of women went to work in the factories and industries that had converted to full time war production. Food and raw materials such as rubber and oil were rationed and sacrificed. It is an easy conclusion to draw that WWII had affected every American. Like the previous generation, this last war was seen as the war to end wars. It was the bloodiest in all of humanity. Millions upon millions were killed. Entire European nations were wiped out. In America, returning troops and civilians though America had fought and won the "good" fight. In the late forties, and entire