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The USA & Events in Korea, 1950–53

Exam code: 2147
Written by: Ashika|Reviewed by: Caroline Carroll|Updated 2 July 2026

Causes for the Korean War

Causes for the Korean War

A political map of the Korean Peninsula divided along the 38th Parallel. North Korea is shaded in red with its capital, Pyongyang, marked by a black star. South Korea is shaded in blue with its capital, Seoul, also marked by a black star. China is shown to the northwest in grey. The dashed line labeled "38th Parallel" represents the division between North and South Korea established after World War II.
A map showing how Korea was divided in 1945

  • In 1905, Japan owned Korea

  • In 1945, Japan surrendered to the Allies, ending the Second World War

    • Soviet troops were in the north of Korea

    • US troops were in the south of Korea

  • The terms of Japan’s surrender included the division of Korea

    • The Allies split Korea into two territories along the 38th Parallel

      • This divided Korea into two equal-sized zones

      • Historians believe that Korea was divided to prevent the USSR from taking the whole of Korea

    • The USSR monitored North Korea

    • The USA oversaw South Korea

  • Both the USA and the USSR chose leaders for their sections of Korea:

A visual comparison of the leadership in North and South Korea after the division. On the left, under the red label "North Korea," is Kim Il Sung with a speech bubble saying, "I am the legitimate leader of the whole Korea!" He is labeled "unelected" and is shown to be backed by the Soviet Union, represented with the USSR flag. On the right, under the blue label "South Korea," is Syngman Rhee with a similar speech bubble claiming legitimacy. He is labeled "unelected," "corrupt," and "unpopular," and is shown to be backed by the United States, represented with the American flag
An illustration showing key information about the leaders of North and South Korea

  • In April 1950, many South Koreans voted in favour of the reunification of Korea

    • Rhee was an unpopular leader

    • Many Koreans wanted to reunite their country under the Communist Kim Il Sung

  • In June 1950, North Korea invaded South Korea

    • North Korea had the support of the USSR and China

      • Both countries sent financial and military aid

      • North Korea’s army was more powerful than South Korea’s

Why did the USA Get Involved in the Korean War?

Why Did the USA Get Involved in the Korean War?

Reason

Why did this cause US intervention in Korea?

Domino Theory

The USA wanted to stop Korea from falling to Communism. They believed that if Korea fell, Japan would be next

Trade with Japan

Japan was an important market for US exports. The USA wanted to protect Japan’s capitalism

Truman Doctrine

In 1947, Truman declared that the USA would protect any country in threat of a Communist uprising. The US public put pressure on the government to protect South Korea

Distrust of the USSR 

The USA blamed the USSR for North Korea’s actions. The USSR  had acted aggressively in Eastern Europe and blockaded Berlin

Belief in victory

The US government believed that China would not react if they sent troops to Korea. They hoped that they could persuade the UN to provide military support to South Korea

The UN Involvement in the Korean War

The UN Involvement in the Korean War

  • The USA persuaded the UN to intervene in the Korean War because:

    • Truman placed pressure on the UN Security Council

      • The USA contributed the most money to the UN budget of any other country

      • It could threaten to lower their contribution if the UN did not support South Korea

    • The USSR boycotted the UN in January 1950

      • The USSR  demanded representatives of the Communist People’s Republic of China in the UN Security Council. The UN refused

      • The boycott meant that the USSR could not veto action against North Korea

  • The UN agreed to send troops to stop North Korea’s invasion

    • 18 member states provided troops

    • The USA sent the most troops under the command of General McArthur. McArthur was:

      • The commander of US troops in Japan in the Second World War

      • Essentially in control of Japan from 1945 to 1951

  • UN forces landed in Inchon in September 1950

The Events of the Korean War

The Events of the Korean War

A vertical flowchart outlining the main phases of the Korean War from 1950 to 1953, with each phase numbered and color-coded: June – September 1950 (orange): The North Korean People’s Army makes major advances, forcing South Korean forces to defend only a small area around Pusan. September – October 1950 (green): UN forces, led by General MacArthur, push North Korean troops back to the Yalu River near the Chinese border. November 1950 – January 1951 (purple): In response to the threat of invasion, Mao orders Chinese forces to support North Korea. They recapture Seoul, and UN forces retreat behind the 38th Parallel. January – July 1951 (yellow): UN forces retake Seoul. MacArthur asks President Truman to authorize a nuclear attack on China. Truman refuses, fearing Soviet retaliation, and fires MacArthur. July 1951 – July 1953 (red): The war reaches a stalemate on land but continues in the skies. Dwight Eisenhower becomes U.S. President and promises to end the war. Stalin’s death in 1953 leads North Korea to agree to an armistice. Each stage is linked by arrows to show the chronological progression of events.
A flow diagram showing the key events in the Korean War, 1950-53

Consequences of the Korean War

Consequences of the Korean War

  • The Korean War had several positive and negative consequences for the USA

Positive consequences

Negative consequences

The peace treaty kept Korea divided. The USA had ‘protected’ South Korea from Communism. This was a success for containment

North Korea remained Communist and formed closer ties to China. This shows that following containment could stop but not push back Communism

The UN stood up against North Korea’s aggressive actions. This made the UN more successful than the League of Nations had been before the Second World War

The Korean War caused four million casualties and the deaths of 50,000 US soldiers. The USA had underestimated the impact of fighting against Communism

The USA created anti-Communist alliances in Southeast Asia (SEATO) and Central Asia (CENTO). The USSR felt surrounded by enemies 

Tensions increased between the USA and the USSR. Both began a nuclear arms race, creating hydrogen bombs and ICBMs. This threatened world peace

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