The collapse of the USSR wasn't caused by economics or arms races - see how regimes like Cuba, North Korea still survive. Low oil prices helped, but it could have happened during a boom, too. The 80s were not the worst economic or humanitarian crisis the USSR has faced, not even close. The Soviet Union collapsed because the Party lost control of the country and the tensions and outright conflicts that previously prev…
We (the US) were able to trigger an arms race at a time when the Union was least able to afford it, and overwhelm what central planning could deal with.