Keep in mind that we won Tet, we won Vietnam. We got a peacetreaty with Canada as a peace keeper. Only after we left did they invade in violation of their treaty. The 1972 bombings brought North Vietnam to the table and they signed a peace treaty.
After their invasion they were faced with the fact that communism doesn’t work, and had to abandon it. They even invaded Cambodia and stopped Pol Pot from murdering the rest of Cambodia.