Where to even begin? Yugoslavian regional desires? Vietnamese Doi Moi and how it emerges from Le Duan and how that stems from the differences in the north and the south’s unequal development despite a common struggle? Che’s writings on USSR/Cuba/Free Trade/Sugar? Defining what differs between Khrushchev or Deng(its nothing)? How soviet “social imperialism” is in retrospect clearly subordinated to American imperialism and now China repeats the same mistakes today. The eurocommunism-maoist split and how that really does derive from various European communist parties and just about every single USA communist parties revisionism, which plays out now in various rightist deviations towards what “actually exists” and from that “what is actually possible”.
And of course all of this precedes the answer to why post colonial bourgeois nationalism flared up in border struggles with Vietnam and China, and now regrettably we have a china that continues many of these trends. Laos and Vietnam still at least exist as a good model of interstate relations, or much of the Soviet unions internal borders at least before capitalist restoration and the return of genocidal ambitions we see today.
not to be trite with you, this question is massive, and arguably as fundamental to communism as any other question nowadays, given its real applicability on how revisionism re-asserts itself time and time again, although its particular contours are obviously not at all limited to “who gets to own a couple islands along the amur river”. No easy book to start with, but Albania-China relations is probably as good a starting point as any.
The point that the USSR would have invaded China due to the cultural revolution(or perhaps you are referencing something else I am completely unaware of) is absurd. It only intervened when bourgeois counter-rev was impending within the warsaw pact when it was invited.
The real nature of the question here is not persay the thought process behind how someone could mistake the USSR as an imperialist power equal to the USA, but how the theoretical underpinnings there intertwined with the great proletarian revolutions struggles within military politicization. Once we have that we do not have to throw the idea away wholesale, and it certainly ties into social imperialism in a real sense, and SPD’s being critiqued by Lenin as an origin of that phrase. I do not have persay finalized thoughts there.
To your second point it feels a bit callous to list off a couple points and not grapple with the fundamental failure of decolonizing the world along socialist lines. Certainly China, the USSR, and Mongolia were able to draw reasonable borders all together, but the sino-vietnam-cambodia war is just one example that is clearly formed by colonialism and chinese revisionism and persists to this day. And that underlying issue, not making up a tally of W’s and L’s, is what I am interested in. But certainly point taken that successes are possible, although quite a few of them likely have to due with quelling nationalistic urges in border regions more so than socialist-oblige.