The civil wars in Korea, Vietnam, and China were peasant/working-class revolts against the wealthy ruling class. The poor fought for communism and socialism because they offered equality, but the US intervened on behalf of the ruling class, who were the minority.

US history tells an entirely different story than Korean history, and when I get the chance I'll provide links. If I remember correctly, 82% of Koreans preferred communism in the 1950s. Academic research papers provide the data, but they're often locked behind paywalls.

Oh! If you have a library card you should have access.