I'm thinking that if the NVA had bases in Cambodia or Laos and neither government did anything about it, either they were too weak and therefore needed our help to repel the NVA or they were harboring the enemy.
In either case, it should've been acceptable, right?
I understand that Nixon was under popular pressure to reduce or end the war. I don't know how significant that was to the policies controlling the strategy.
Is there actually anything in international law about this? I assume that the USA would have had military bases in a lot more countries than North Vietnam. Could a US Army base in, for example, West Germany or Turkey ever have been a legitimate target for the North Vietnamese Army if they had the ability to stage a military attack over such a distance?
In either case, it should've been acceptable, right?
I'm not sure who exactly you mean it should have been acceptable to? If you mean the American public, expanding the war into Cambodia seemed to contradict his stated policy of withdrawal from the war.
Cambodia was ostensibly a neutral country, at least until just before the March 1970 coup. Invading neutral countries is generally seen in a poor light. The invasion has since been condemned as it resulted in NAVN and NLF troops spreading out all over Cambodia rather than sticking to border areas.
The demographics of:
-North Vietnam: 19 to 22 million
-South Vietnam: 15 to 19 million
-Laos: 2,5 million
-Cambodia: 5 million