The Cold War developed due to mistrust between the United States and Soviet Union after WWII. The US feared Soviet expansion while the Soviets wanted to rebuild and gain influence. This led both sides to build up their militaries. The US policy of containment sought to block Soviet influence without direct war. Events like the Berlin Blockade and Korean War escalated tensions, while NATO and the Warsaw Pact divided Europe between the allies. By the 1960s, the superpowers were engaged in an arms race and proxy conflicts in the developing world.