On June 27, 1950, the United States officially entered the Korean War. The U.S. supported the Republic of Korea (commonly called South Korea), in repelling an invasion from the Democratic Republic of Korea (commonly called North Korea).
 
The Korean War was a conflict that emerged after World War II. The Empire of Japan had occupied the Korean Peninsula during the war. After Japan’s defeat, the victorious Allies split the peninsula on the 38th parallel. U.S. troops occupied the southern part, while Soviet troops occupied the northern part. The two Koreas engaged in border conflict, which escalated when North Korea invaded South Korea on June 25. 
 
The Korean War was a proxy war for the Cold War. The West—the United Kingdom and the U.S., supported by the United Nations—supported South Korea, while communist China and the Soviet Union supported North Korea. The Korean War ended three years later, with more than 600,000 casualties (about 36,000 Americans). The war ended with virtually no change in the border.
 
The Korean Peninsula is still divided, with military personnel from both North and South Korea occupying the demilitarized zone (DMZ).
Allies
Noun

alliance of countries that opposed the Axis during World War II. The Allies were led by the U.S., the United Kingdom, and the Soviet Union.

Noun

natural or artificial line separating two pieces of land.

Cold War
Noun

(1947-1991) conflict between the Soviet Union (and its allies) and the United States (and its allies). The two sides never confronted each other directly.

communist
Noun

person or group of people who support communism, a type of economy where all property, including land, factories and companies, is held by the government.

conflict
Noun

a disagreement or fight, usually over ideas or procedures.

defeat
Verb

to overcome an enemy or obstacle.

demilitarized zone (DMZ)
Noun

area not controlled by any government, and where it is illegal to station troops.

emerge
Verb

to develop or come into view.

empire
Noun

group of nations, territories or other groups of people controlled by a single, more powerful authority.

escalate
Verb

to increase.

invasion
Noun

an attack or move to take possession.

military
Noun

armed forces.

occupy
Verb

to take control of a place, usually by force.

parallel
Noun

line of latitude, dividing the Earth by east-west.

Noun

piece of land jutting into a body of water.

proxy war
Noun

conflict where countries indirectly oppose each other by supporting different sides in another conflict.

repel
Verb

to resist or push back.

Soviet
Adjective

having to do with the Soviet Union and the areas it influenced.

support
Verb

to provide emotional, intellectual, or material encouragement or approval.

troop
Noun

a soldier.

United Nations
Noun

international organization that works for peace, security and cooperation.

victorious
Adjective

having won.

virtually
Adverb

almost or nearly.

West
Noun

having to do with the developed nations of Europe and North America.

World War II
Noun

(1939-1945) armed conflict between the Allies (represented by the United States, the United Kingdom, and the Soviet Union) and the Axis (represented by Germany, Italy, and Japan.)