The United States turns to a Socialist/Social Democratic State in this timeline. This is mainly due to an earlier depression and due to less of a Red Scare due to the Bolsheviks failing to win in Russia (Kolchak won eventually). Jiang Jieshi of China manages to successfully kill the Chinese Communists due to a lucky break during the Long March, where Ma Troops managed to sucker punch and kill off the escaping soldiers and leaders. This sets the stage to the Viet Nam War, which happened after the violent First Decolonization Wave happened.
The US under the Socialist Labor party intervenes in Viet Nam in the early 1960s, which is undergoing a civil war. The North, being supported in part by the Kuomintang who wanted to support a friendlier face in the region, was doing well against the South, led by Ho Chi Minh, a pragmatic leader who adopted Communism to create a free and powerful country. The US cooled relations with China at this time and did not want to lose a friendly face in the region, so were willing to send support to counter the Chinese. Nam was the result of the Anti-imperialist rhetoric of the White House, which staged a successful stalemate in Korea in spite of Russian intervention during the 1950s.
It took years and the collapse of Jiang Jieshi's government (never exactly that strong to begin with) to win, but by 1973, the People's Republic of Vietnam was successful in unifying South with North. Much of the success was due to the spirit of the Vietnamese and the relative competence of Ho Chi Minh, who died one year before his dream came true. Vietnam was a polarizing war in the US, but acknowledged as "Doing the Right Thing". This would have dire consequences when the USA intervened in the collapse of the Pahlavi Shahdom of Iran, which was a far bloodier affair.