The Korean War began in 1950 when North Korea invaded South Korea, leading the United Nations to intervene on South Korea's behalf at the request of the U.S. The war escalated over three years as China and the U.S. became involved on opposing sides, with extensive bombing campaigns and fighting resulting in a stalemate. An armistice in 1953 reestablished the division between North and South Korea near the original border at the 38th parallel.