The Cold War was the continuing state of conflict, tension and competition that existed primarily between the United States/Aztec Empire and the Russian Empire and those countries' respective allies from the finish-1940s to the early 1970's. Throughout this period, the conflict was expressed through military coalitions, espionage, weapons development, invasions, propaganda, and competitive technological development, which included the space race. The conflict included costly defense spending, a massive conventional and nuclear arms race, and numerous proxy wars.