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United States Involvement in the Korean War: Causes and Effects

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  • 0:05 Korean War Causes
  • 1:13 The War Commences
  • 2:57 The Tide Shifts
  • 4:01 China Enters the War
  • 4:47 Forging an Armistice
  • 6:04 Lesson Summary
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Lesson Transcript
Instructor: Adam Richards

Adam has a master's degree in history.

The Korean War was a short but bloody war with more than five million casualties. Find out what caused this deadly and destructive war, how the United States came to be involved and how the war affected Korea and its allies.

Korean War Causes

The end of the Second World War meant peace and prosperity for Americans and many other people around the world. Yet, for the Koreans, it represented difficulty. Korea was part of the Japanese empire throughout the first half of the 20th century. When Japan fell during the Second World War, Korea was suddenly free, and hoped to finally be able to decide the fate of their own country. Most Koreans campaigned for a unified state.

However, the United States and the Soviet Union had different ideas. The Soviets wanted to expand the sphere of communist influence into Korea. The United States countered by encouraging the establishment of democracy. Additionally, the United States stressed the importance of containment, which is a foreign policy used to prevent the spread of communism.

This disagreement would eventually lead to the Korean War. The Korean War was the first battle of the Cold War, and first major proxy war fought between the United States and a Soviet communist supported enemy. A proxy war occurs when one or more opposing powers instigates a war and then uses third parties to fight on their behalf. Other examples of proxy wars include the Vietnam War and the War in Afghanistan.

The War Commences

At the Potsdam Conference in 1945, the Allies decided to split Korea into two parts at the 38th parallel. North Korea became a Soviet-supported communist regime under the leadership of Kim Il-sung; South Korea became a U.S.-supported democratic state under Syngman Rhee.

After the division of Korea, Kim Il-sung looked to unify the nation. He garnered support from the Soviet Union and China to launch an invasion in South Korea, and remove those who supported Syngman Rhee's appearance of democracy. Armed with Soviet rifles and tanks, North Korea crossed the 38th parallel on June 25, 1950; the war was underway.

President Harry Truman viewed the situation as more than just a war between two nations. He feared the North Korean strike was the first step in an international communist takeover led by the Soviet Union. In response, Truman cited a 1950 National Security Council report known as NSC-68, which called for military force to contain communism. The President and other top officials saw the conflict as an opportunity to declare war against communism. Therefore, with support from the United Nations, the United States moved to establish peace, and remove the communist invaders from South Korea.

The early engagements were negligible. The United States, and its affiliated forces, lacked an efficient strategy during the onset of the Korean War, not to mention the American soldiers found the terrain and weather extremely difficult to conduct operations in. Additional pains were caused by the inefficiently trained and poorly led South Korean army. By the beginning of September, North Korean forces had advanced all the way to the Tsushima Strait on the border of South Korea. The North Korean march also successfully captured Seoul, the capital of South Korea.

The Tide Shifts

The early victories of the North Koreans were short lived. By mid-September, the United States had turned the North Korean advance by utilizing its arsenal of sophisticated weaponry. Simultaneously, Truman authorized General Douglas MacArthur, Supreme Commander of the United Nations forces, to take whatever measures necessary to push the North Koreans back across the 38th parallel.

MacArthur recommended an amphibious landing at Inchon in South Korea. On September 15, MacArthur landed over 10,000 Marines at Inchon. By the end of the month, American forces had recaptured Seoul and began the process of driving the enemy out of South Korea. With American success came MacArthur's desire to pursue war into North Korea, and eliminate the enemy completely.

Truman was hesitant to honor MacArthur's request because the President wanted to maintain a limited engagement in Korea. Total war was not an option for the United States because Truman did not want to encourage a Chinese entry into the war. Additionally, this war was meant to contain the communist enemy, not eradicate them. Notwithstanding his reservations, Truman allowed MacArthur to carry the war into North Korea.

China Enters the War

MacArthur successfully crossed into North Korea in November and pushed his forces to the Yalu River, which is the border of North Korea and China. This was a fatal mistake on the part of MacArthur because China viewed the advance as overly aggressive. As a result, China entered the war on the side of North Korea. The Chinese successfully drove MacArthur's forces back across the 38th parallel. Eventually, MacArthur was able to regain the initiative and drove the Chinese back across the divide.

With the war back in the favor of the United States, Truman encouraged MacArthur to negotiate a settlement. However, MacArthur rejected Truman's request in favor of total war against North Korea and China - even if it meant the use of nuclear weapons. Infuriated with his Supreme Commander, Truman relieved MacArthur from command.

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