The Viet Nam war, one where I served two tours required us to get permission from the UN Secretary of Security before attacking North Viet Nam. We were forbidden to attack any place within 20 miles of the Gulf of Tonkin coastline for fear that we might kill a Russian. Whenever the fighting slowed due to the north running low on ammo there would be diplomatic discussions held and fighting would cease until they were resupplied.
I also served two tours in Vietnam including one year in-country during the Tet Offensive. I suggest you check some of your facts.
What facts need checking?
Simply not true. We never received or sought UN approval to go into Vietnam or to attack North Vietnam.
We were forbidden to attack any place within 20 miles of the Gulf of Tonkin coastline for fear that we might kill a Russian.
Forbidden by whom? Certainly not by the UN. Operation Rolling Thunder went on from March 2, 1965 until 2 November 1968. McNamara set limits. Airstrikes were strictly forbidden within 30 nautical miles (60 km) of Hanoi and within ten nautical miles (19 km) of the port of Haiphong. These were later lifted. We bombed Cambodia and Laos as well.
There is no doubt that Russians and Chinese were manning some of the anti-aircraft batteries and flying some of the aircraft against us. We were not fighting to win, but to keep South Vietnam free from being taken over by the North. It was a disgrace the way we exited the war leaving the South Vietnamese to fight on for over two years alone. We eventually cut off our supplies to them and did nothing when the North violated the Paris Peace Accords by staging a full scale invasion in 1975 that eventually led to the defeat of the South.
Fighting a war incrementally and escalating it gradually was a terrible way to fight a war. And the politicians like Johnson and McNamara were micromanaging our prosecution of the war. We never lost the war on the battlefield. It was lost in Washington.