The first American intervention following World War II, was in Korea. The USSR was allied with North Korean communists, while South Korea was allied with the USA. "Both superpowers met at the 38th parallel...they agreed to split and occupy Korea along that line" (Dean). The war began in 1950, when North Korea invaded Seoul in South Korea (Abhinav). The United States had previously decided not to arm the South, allowing North Korea to easily invade and capture Seoul. The United States decided to intervene in Korea to protect the sovereign rights of South Korea ("The Korean War: United").
North Korea invades South Korea
America declares its intention to intervene in Korea