From Ohio History Central
The Korean War was one of several military conflicts that occurred during the Cold War, as the United States and its allies attempted to stop the spread of communism.
This conflict began on June 25, 1950, when North Korea, a communist nation, invaded South Korea. Prior to World War II's conclusion, North and South Korea had been a single country known as Korea. After the war, Korea became two countries. By invading South Korea, North Korea hoped to reunite the two nations as a single country under communism.