The Cold War was the strained relationship between the U.S. and U.S.S.R. from 1945 until the collapse of the Soviet Union in 1991. Key events included the Berlin Blockade, Marshall Plan, NATO alliance, Korean War, Cuban Missile Crisis, and arms limitation treaties. The Cold War was characterized by ideological and military tensions but no direct armed conflict between the two superpowers, as both had nuclear weapons leading to the threat of mutual destruction. The relationship transitioned to détente in the 1970s and ended with the dissolution of the Soviet Union in 1991, bringing the bipolar world to a close.