The Korean War was a result of the division of Korea making it into North Korea and South Korea. During World War II the United States decided that it was going to occupy the southern half of Korea to protect the peninsula from communism. The U.S.S.R., with help from China, decided to occupy the northern half of Korea. North Korea was ruled by Kim Il Sung, and South Korea was ruled by Syngman Rhee. The United States and the Soviet Union joined forces with the people of Korea in the halves they were occupying to build regimes that supported their interests, and North Korea was communist and South Korea was not communist.

Even though this was happening, North and South Korea's division wasn't formalized until 1948. In 1948, North Korea became People's Republic Of Korea, and South Korea became Republic Of Korea. Korea was divided at the 38th parallel. The Americans chose to divide it this way because it would keep Seoul the capitol city on the American occupied half. By 1949 the Soviet Union and the United States had removed all their troops from North and South Korea. May through December 1949 there were many skirmishes on the border between North and South Korea. On June 25 , 1950 North Korea invaded South Korea by crossing the 38th parallel. North Korea made a statement saying that South Korea had already opened fire and crossed the 38th parallel attacking North Korea and that North Korea had fired back in defense. This claim has not yet been proven.

The United States supported South Korea and were later joined by troops from the United Nations, and contingents of British, Canadian, Australian, and Turkish troops. The Soviet Union and China joined in to help North Korea. When North Korea made this attack on South Korea their plan was to win the war in a month. Their plan had almost succeeded. By the end of July, North Korea occupied about 90% of the land in Korea. However, the plan didn't succeed, because South Korean forces managed to win back Seoul. This victory reestablished the division of Korea at the 38th parallel where it remained the major battle front until the war ended in 1953.