The Soviet Union collapsed because of massively broken economy. That's just basic science. They exported oil and imported grain. Russia imported GRAIN for gods sake. Then oil prices collapsed. Next? They did nothing and just ate through the resources until they were no more.
And then 'evil liberals/evil west destroying the great country' happened, when finally USSR had no money to pay for the social obligations and for massive military.
This are the undisputed facts, supported by a vast trove of internal documents from the late USSR and first years of the Russian Federations.
A monograph by Egor Gaidar [1] is an excellent source referencing tons of the original documents.
Sorry for Russian, not sure this is available in English anywhere.
I get that it's easier to think that source of our problems is some evil mastermind and conspiracy. But think of the Occam's razor — this is explained much easier by sheer incompetency and stupidity and no checks and balances to mitigate them.
1. https://ru.wikipedia.org/wiki/Гибель_империи_(монография)