Korean War, or Korean Conflict, 1950–53, a war fought between the Republic of Korea (South Korea) and United Nations forces on the one hand and the Communist-dominated Democratic People's Republic of Korea (North Korea) and Communist China on the other. The war began June 25, 1950, with a North Korean invasion of South Korea. It ended with an armistice signed July 27, 1953, neither side having achieved a decisive military victory.

In a broad sense, the Korean War resulted in a United Nations victory because the aim of forcing back the aggressors was achieved. However, the war ended, as it began, with Korea divided, and the issues behind the war were not resolved.

The Korean War was the first war in which troops of an international body—the United Nations—fought. Most of the UN forces were provided by the United States, but 20 other UN countries also supplied troops, naval forces, air support, or medical aid. At the time the war was being fought it was officially referred to in the United States as a “conflict” because there was no declaration of war by Congress. President Truman referred to it as a “police action.”

The war was fought largely with the weapons of World War II. (No nuclear weapons were used, however). Its tactics, after the initial stages, were somewhat like those of World War I. New weapons were tested only in the air, where jet fighters fought each other. Communist charges that the United States used germ warfare were false.