Cold War competition began between the U.S. and the Soviet Union right after the end of World War II, when its alliance unraveled.
During World War II, the U.S. and the Soviet Union were united by a common goal of defeating Nazi Germany. However, once the war concluded in 1945, deep ideological differences surfaced. The United States championed capitalism and democracy, while the Soviet Union promoted communism and a one-party state. Disagreements over the reorganization of post-war Europe, the fate of Eastern European countries, and differing visions for world order led to rising tensions. Key events, such as the Iron Curtain speech by Winston Churchill in 1946 and the subsequent establishment of Soviet-backed regimes in Eastern Europe, solidified the divide and set the stage for the prolonged geopolitical rivalry known as the Cold War.