The primary cause of the Cold War was the ideological conflict between the United States and the Soviet Union following World War II. The U.S. championed capitalism and democracy, while the Soviet Union promoted communism and a state-controlled economy. Tensions escalated over differing visions for post-war Europe, leading to an arms race, the formation of opposing military alliances (NATO and the Warsaw Pact), and numerous proxy wars. The fear of the spread of communism in the West, particularly evident during events like the Korean War and the Cuban Missile Crisis, solidified an atmosphere of distrust and hostility that defined global politics for decades.