Cold War (1947–1991) - The Cold War was the state of conflict, tension and competition that existed between the United States (US) and the Soviet Union (USSR) and their respective allies from the mid-1940s to the early 1990s. Throughout this period, rivalry between the two superpowers was expressed through military coalitions, propaganda, espionage, weapons development, industrial advances, and competitive technological development, e.g., the space race. Both superpowers engaged in costly defense spending, a massive conventional and nuclear arms race, and numerous proxy wars.
The Cold War drew to a close in the late 1980s and the early 1990s. With the coming to power of US President Ronald Reagan, the US increased diplomatic, military, and economic pressure on the Soviet Union, which was already suffering from severe economic stagnation. In the second half of the 1980s, newly appointed Soviet leader Mikhail Gorbachev introduced perestroika and glasnost. The Soviet Union collapsed in 1991, leaving the United States as the sole superpower in a unipolar world.