Communism vs. Capitalism

It would be easy to dismiss the Cold War simply as proof that Capitalism was a better theory than Communism. Easy, but not the whole story. In order for Communism to be relegated to the dustbin of history, it first had to be proven that its struggle against Capitalism was unnecessary and thus irrelevant. How did the US and the USSR close the gap in the last quarter of the 20th Century to allow Communism to go out with a whimper and not a bang?