Those Involved: Communist forces led by Kim Il Sung (North Korea) backed by the Soviet Union and Nationalist forces led by Syngman Rhee (South Korea) backed by the U.S.
What is it: During this time the U.S. and the Soviet Union agreed to not have rivalries with one another and decided to occupy and plant territories on the Korean peninsula. America had South Korea and the Soviet Union had North Korea. The North Korean leader Kim Il Sung wanted to have all of Korea to be ran by him and have Communist laws. Il Sung wanted aid from the Soviet Union, however, they were reluctant in the beginning. After Il Sung kept urging Stalin to help North Korea with forcing to make South Korea a Communist nation and to be all as one, Stalin eventually gave in and helped. Which is what started the Korean War.
Significance: It’s significant to the Cold War because the U.S. had no choice but to intervene and help protect South Korea. It started with North Korea launching a surprise attack across the 38th parallel line which resulted in President Truman having to order the UN security council to authorize police action against North Korean troops. Since U.S. troops were sent to South Korea to help prevent the invasion of North Korean soldiers coming into the country, U.S. troops pushed boundaries into China and started turmoil with them. The Chinese attack set ground rules for the conflict of the cold war. Truman eventually dismisses American General MacArthur and that leads to Turman proposing a peace agreement between China and the U.S. for invading the Yalu River. The peace agreement with China saved America from being in a costly war with them. The later elected U.S. President Eisenhower left Korea separated, kept South Korea from being a Communist nation, and having a mutual defense treaty between them and the U.S. This was one of the first represented battles of the Cold War in which the U.S. and the Soviet Union had taken opposing sides in a civil dispute.