The US never invaded Vietnam.
The US didn't invade South Vietnam. The Republic of South Vietnam asked for US help as they couldn't stem the Red Tide (communist infiltration).
1944
If we invade North Vietnam, the chances would have been, China & stupid Soviets enter the war and start a WWIII.
The US chose NOT to deploy nuclear weapons. (The US did deploy nuclear weapons against Japan in WWII). The US chose NOT to invade North Vietnam. (The US did invade North Korea during the Korean War).
Yes; invade the north and/or use nukes.
Yes,yes they did.
Could not invade N. Vietnam. Could not use nukes.
1. US could NOT use nukes 2. US could NOT invade North Vietnam 3. US could NOT stop the flow of men/material into RVN
how come the united states did not invade north vietnam to end the war
After the treaty.
Most definitely. Simply had to invade North Vietnam. If the Soviets or Red China intervened; use nuclear weapons against them. Which is why North Vietnam wasn't invaded.