This whole "you need to have multiple political parties who are in constant conflict with eachother in order to have democratic freedom" is an extremely weird western-centric point of view. Does a communist country need capitalist opposition parties? Does a communist country need multiple communist parties? Why would it matter how many political parties there are if the country is otherwise democratic?
A one-party state is the equivalent to a no-party state - yet the emotional response to such a thing is completely different. It begs the question why and I think the answer is extremely obvious to anyone with any sense of historical context. Everyone's opinion starts and ends with "one-party" as if this is some how the only measure of freedom, since that is literally the only extra choice there is in a liberal democracy. The average person in the west has virtually no idea what socialism or communism means other than "one-party dictatorship" because that's literally all the western propaganda powers had to do in order to convince the populace that this is what separated us from them, completely disregarding the fact that dictatorships all over the world were and are still allied to the west and have been propped up by the west. The only thing that mattered to the ruling class in the west was that their dictators were "capitalist" and that was good enough for the average person who imagined that term to be interchangeable with "free".
As far as "nukes establishing their sovereignty" you are correct... which is why there was never a military invasion of the nuclear powers. The way the CIA and other intelligence agencies would work to destabilize the communist countries would be political actions, which would be made incredibly easy in a country that decided to liberalize. Look at what happened to the USSR after the cold war had already died down and tell me they should have done it earlier. None of the countries involved have recovered and every single country is worse off than when they were in the USSR.
No liberal democracy would survive extended economic warfare with the united states much less the entire western world for very long at all. It is not a coincidence that the only countries still standing against them have "strongmen" type governments, because all the "free" countries that stood against them fell extremely fast. The United States didnt accidentally become the world's dominant economic power, they've been forcing their will onto others for a hundred years.