Since the two major fighting powers-US and Soviet Union-both had nuclear weapons, there was a constant threat of nuclear war. Nuclear war never happened in the cold war, but there were many close calls, most namely the Cuban missile crisis. The constant buildup of nuclear arms with both superpowers was the main focus of the cold war-the arms race. A heavy dependence on the Military-Industrial Complex and theories such as Mutual Assured Destruction (MAD) used by President Kennedy and Strategic Defense Initiative (SDI)/"Star Wars" used by President Reagan. Nuclear disarmament was also a main focus of the cold war.