Wait, by CCCP I mean the Союз Советских Социалистических Республик, or the Soviet Union.
Ok, Laos and Cambodia were weak states, but Vietnam was any stronger than them? Sure we achieved a polictical victory against the US and destroyed the South Viet govt, but Vietnam or any countries would never go to war again just after 4 years. At that time, the South Vietnam govt remnaints still lingered in the border, trying to start a reguila war against Vietnam. Many South Viet civilians resisted the establishment of communist rule. China demanded Vietnam returning food they supplied during war time. Vietnam had to handle many things so why would they started a war? They must have time to rest, to build up force. 4 years were not enough, maybe 10-15 years sound more appropriate, at least when a new generation of population mature. Sure CCCP could give us unlimited supply, but we didn't have enough men to fight for them.
The age of colonies was over after Vietnam beated France. No countries dared to colonize others without interfering from the world community. And expanding Vietnam influence over Indochina? Maybe you had some points here. But there was still a SEATO at that time, and Thailand was a member. And Khmer Rogue was a communist govt so SEATO could care less about 2 communist countries fighting each other, like they give zero fck when Vietnam and China fighting. Now is different from then so is that clear to you?