Kim Il-sung started the war with Stalin's approval and Mao's consent; the USA responded through the UN.
Kim Il-sung repeatedly asked Stalin for permission to invade the south. Stalin refused in 1949, fearing an American response. In early 1950 he agreed, after the communist victory in China, the Soviet atomic test and Acheson's speech suggested the risk was lower. He insisted that Kim also obtain Mao's agreement, which Kim did in May 1950.
On 25 June 1950, North Korean forces invaded the south and quickly captured Seoul. Evidence from Soviet archives, opened in the 1990s, shows the attack was planned with Soviet approval and advisers.
Truman decided that the attack must be resisted. The UN Security Council, which the Soviet delegate was boycotting over China's seat, condemned the invasion and called on members to help South Korea. US forces fought under a UN command led by General Douglas MacArthur.
On 27 June, Truman also sent the US Seventh Fleet into the Taiwan Strait. He increased aid to the Philippines and to the French in Indochina. The response was regional containment in Asia, not only the defence of Korea.
- Invasion
- 25 June 1950.
- Soviet boycott
- Allowed UN Security Council resolutions to pass.
- Seventh Fleet
- Sent to the Taiwan Strait, 27 June 1950.
Worked example: Explaining Stalin's change of mind
Why did Stalin approve the invasion in 1950 after refusing in 1949?
- Balance of power: the Soviet atomic test in August 1949 ended the US monopoly.
- Asia: the communist victory in China strengthened communism in the region.
- US signals: Acheson's speech suggested Korea was outside the US defensive perimeter.
- Risk-sharing: Stalin required Mao's consent, so China would carry the burden if the war went badly.
Watch out for this
The Soviet Union planned the Korean War and forced Kim to invade.
Kim initiated and pushed for the war. Stalin approved and supported it, and Mao consented, but the drive came from Kim's aim to reunify Korea.
Check your understanding
Why could the UN Security Council act quickly against North Korea in June 1950?
- The Soviet delegate was boycotting the Council and could not veto.
- The USSR voted in favour.
- China used its veto to support action.