The Korean War began in 1950 with the invasion of South Korea by North Korea. The United Nations, with the United States as the principal force, came to the aid of South Korea. China intervened on behalf of North Korea, and Soviet Union provided air support. United Nations forces pushed the North Koreans back across the 38th parallel but could not break through to capture Pyongyang, which was well defended by Soviet-built weapons.
The fighting ended in 1953 after an armistice was signed; no formal peace treaty has ever been signed between North and South Korea.
In June 1950, American planes were sent to fly reconnaissance missions over North Korea; they were chased away by North Korean MiG fighters. On June 25th, two U.S. Navy destroyers were attacked by North Korean torpedo boats off the coast of South Korea; one destroyer was hit but both ships escaped without damage.
On June 27th, President Truman announced that he had ordered American troops into South Korea to protect it from communist aggression; this action violated a treaty he had signed with China in 1945 not to send troops into Korea without its permission. In response to this attack on their territory by Americans (who had not yet invaded),