Early Cold War: 1945–1962

Korean War

Causes and Effects of the Korean War

The Korean War was fought between the United States and its allies and the Soviet Union and its allies over the 38th parallel, the line dividing Soviet-supported North Korea and U.S.-supported South Korea.

The causes of the Korean War (1950–53) can be traced back to the end of World War II. Seven days before Japan surrendered, the Soviet Union declared war on Japan and sent troops to fight the Japanese on the China/Korea border. When Japan surrendered, by agreement there was a temporary division of Korea with a demarcation line, the boundary or border of a specific area, set at the 38th parallel. U.S. forces accepted the surrender of Japan's troops south of the 38th parallel, and the Soviet Union accepted their surrender north of the parallel. Afterward the Soviet Union quickly closed the 38th parallel border and established a government, while a U.S. military government governed south of the 38th parallel. The United Nations (U.N.), an international organization founded in 1945 to maintain peace and security throughout the world, called for free elections throughout Korea in 1948. The Soviet Union, however, refused to allow U.N. election officials into the north. South Korea held elections and established a democracy, the Republic of Korea (South Korea), on August 15, 1948. The Soviet Union changed the north's name to the Democratic People's Republic of Korea. Soviet forces withdrew in 1948, leaving behind a communist dictatorship and a well-equipped army. American forces left South Korea in 1949, leaving behind a weak democratic government and an ill-equipped army.

The Korean War began on June 25, 1950. It pitted invading North Korea, with its allies the Soviet Union (which had acquired nuclear weapons) and China, against South Korea and its allies, a joint U.N. force led by the United States. The war was marked by stunning victories and defeats on both sides. A peace conference began in July 1951, but a stalemate, a situation in which neither side has the opportunity to advance, lasted two years. An armistice, an agreement to end a war, was finally signed on July 27, 1953. The treaty kept the 38th parallel division but created a demilitarized zone (DMZ), an area free of weapons and military forces, around the parallel.

Major Events of the Korean War (1950–53)

Over a span of three years, U.N. forces led by the United States fought a series of battles against the Soviet and Chinese allies of North Korea, with neither side gaining the advantage. The armistice guaranteed the preservation of the 38th parallel but as a demilitarized zone.

Major Events of the Korean War

Date Event Result
June 27, 1950 U.N. Security Council votes for members to assist South Korea. Sixteen U.N. nations, including the United States, form an alliance.
September 12, 1950 North Korean troops reach their farthest point south, the southeastern Port of Pusan. North Korea controls most of South Korea.
September 15, 1950 The United States makes a successful amphibious landing in Inch'ŏn, 150 miles north of the 38th parallel. U.N. troops are stationed in North Korean territory.
October 25, 1950 U.N. troops reach Yalu River on the border of North Korea and China. U.N. troops gain control of most of North Korea.
November, 1950 Large Chinese unit strikes U.N. troops near Yalu River. The United States, fearing a nuclear war with China and the Soviet Union, accepts the division of Korea.
November-December, 1950 U.S. marines face off against Chinese forces in the Battle of the Chosin Reservoir. Vastly outnumbered, the marines fight their way back to their supply ships in a battle lasting 17 days. This becomes a defining moment for the U.S. Marine Corps.
March 14, 1951 U.N. forces liberate Seoul, South Korea's capital, for the fourth and last time. U.N. forces occupy much of South Korea.
July 27, 1953 The armistice is signed. The 38th parallel is maintained but is surrounded by a demilitarized zone.

Korea During the Korean War, 1950-53

During the Korean War of 1950-53, control over territory often changed between North Korea and South Korea and their respective allies, China and the United States.