The Korean War was a conflict that lasted from 1950 to 1953 and involved North Korea, South Korea, and the United States. The war began when North Korean forces invaded South Korea in an attempt to reunify the Korean peninsula under communist rule. The United States, along with other United Nations forces, intervened to support South Korea and prevent the spread of communism. One of the most significant developments during the Korean War was the emergence of nuclear weapons as a potential factor in the conflict.