what you refer to as
real life versions of communisms are in fact attempts to establish communism by communist parties within their respective nation states. communism has bever been reached - and none of these parties in power ever said that they had.
the way you use the word (associating USSR, China, Cuba, N Korea with communism) is the result of cold war propaganda. more accurate terminology for these (horrible!) dictatorships would be authoritarian regime with state-monopolized capitalist economy.
all summarized communism is an ideal economy where each gives what they can and gets what they nees, where necessity is at the core and not the accumulation of wealth.
could you at least say what you are quoting when using citations for your argument?
that being said: collective ownership of the means of production (what socialism means) is a direct contradiction to nation-states as long as these are unable to reflect the collective will within their structures.