On June 25, 1950, North Korean troops invaded the South, sparking the three-year Korean War. The North argues the invasion was in retaliation for the U.S.'s brutal incursions into their territory.

Shortly after the attack, the United National Security Council passed a resolution calling for an end to North Korean aggression.

After a call to aid the Republic of Korea, U.S., U.N. and South Korean troops under the command of Gen. Douglas MacArthur, responded by seizing around two-thirds of the country.

But North Korean troops, with the aid of the Chinese People's Volunteer Army, successfully pushed back South Korean and U.S. forces to the 38th parallel. Chinese communist leader Mao Zedong dispatched millions of Chinese troops to North Korea, concerned U.S. forces would invade China if it triumphed over North Korea.

Both forces eventually reached a stalemate, roughly in the area along the 38th parallel.

Truce negotiations began in July 1951, and the talks continued for two years before an armistice agreement was reached on July 27, 1953.

There has never been an official treaty to end the war; the ceasefire agreement has held the uneasy peace for over 50 years.

-- Compiled by Liz Harper for the Online NewsHour