The Cold War emerged after World War II as the United States and Soviet Union emerged as superpowers with influence over their respective allies in Europe and other parts of the world. This led to the division of Europe into Western and Eastern blocs aligned with either the US or USSR, along with an arms race and proxy conflicts between the two sides around the world over the following decades. Key events included the Korean War, Cuban Missile Crisis, Soviet invasion of Afghanistan, and rise of Reagan's military buildup, until the decline and collapse of the Soviet Union in 1991 ended the Cold War.