US rules of engagement were partially to prevent Chinese intervention in the Vietnam War. The Chinese already had 100,000 advisors in the country in an anti-ai

US rules of engagement were partially to prevent Chinese intervention in the Vietnam War. The Chinese already had 100,000 advisors in the country in an anti-aircraft role and a full scale invasion of Hanoi by US Marines would have almost certainly resulted in a response by the PLA. Even though the Chinese troops were poorly armed and poorly trained relative to US troops they had undergone some degree of moderization since the Korean War where they had fought the UN to a standstill. Given the logistical advantages of the Chinese to mass men and material (it was on their border vs half the world away) it isn't obvious the US would have prevailed in a escalated conflict. China was also a nuclear power by 1965 which was not true during the Korean War. But I don't think any of this disagrees with the main point of your comment which is don't intervene where the rules of engagement prevent you from winning.