After the korean war, communism continued to spread. The real question is; how did communism spread to korea? The soviets invaded seoul, north korea, after being informed the us would not be able to come in time. The soviets placed a communist leader in charge of north korea, which soon led to the war Countries such as ,the newly formed, north korea are one of them. The korean war set the precedent for communism as vietnam, laos, and cambodia followed soon after.
In this source of evidence, the United States becomes alliances with the United Nations. They describe the events of how North Korea invaded South Korea in attempt to spread communism. The United States asks the U.N for assistance in this war to the spread.
The video below is just a quick briefing on the concept of Communism