A common enemy can unite peoples of different ideologies.  This was the case of the United States and Russia during World War II.  After Hitler's defeat, it became clear that the relationship between the United States and Stalin's Russia was tenuous at best. Communism and Capitalism just don't mix. 

With the bombings of Hiroshima and Nagasaki, another war was ended, but the world entered the Atomic Age. Russia and the United States deemed themselves "superpowers" and entered into a nuclear arms race. This competition, with all of its paranoia and subterfuge, is know as the Cold War. 

Holden Caulfield's society is one of confused uneasiness.  There is the exuberance that another World War has ended, but there is also the undercurrent that, in fact, it has not ended. Another superpower is building even more powerful atomic weapons and most likely these weapons are aimed at the United States.

Catcher in the Rye was published in 1951.  Take a look at all the timeline of important international events up until that publication date. You should also take a peek at the timeline for nuclear weapon development.