How many times did the US and USSR why was vietnams movement toward communism a threat to the united statescome to engaging in nuclear war?

The US and USSR did not come close to engaging in nuclear war on multiple occasions, notably during the Cuban Missile Crisis in 1962, which was the most significant moment of direct confrontation. Vietnam's movement toward communism was perceived as a threat to the United States because of the "Domino Theory," which suggested that if one country in Southeast Asia fell to communism, neighboring countries would follow, potentially leading to a broader spread of communism. This fear motivated US involvement in Vietnam to prevent the perceived expansion of Soviet influence in the region.