Why did the USSR fall? That's a good question. Many people think that it's because the Berlin Wall fell. Well, that was the trigger for the rest of the dominoes, shall I say. Before the wall fell, there were many things going on behind the "iron curtain" that many didn't know for many years.

The Russian economy was failing. Socialism (other people's money) is great. Until other people's money runs out. Socialism also causes many other things like:
Stagnation in all areas of technology. Which causes:

-Stagnation of the economy (no money to fund research into technology).
     -That also means mass production is set back in all areas, and struggles to keep up with demand. (Not enough food & clothing) 

-You couldn't get fired because of the Socialist Government, so productivity lapsed as well (government workers, sheesh). Remember, everything belonged "to the people", so those making food & clothing, felt over worked and underpaid in a socialist government.

-Then the USSR was also maintaining influence in Eastern Europe, Cuba, the war in Afghanistan, and the costs were continually rising to maintain that influence.

-Then the big one hit, because of the huge costs of maintenance, and they weren't maintaining it, the Chernobyl nuclear disaster happened.

-They also had mixed the left with the right in country, they never allowed them to leave. This bred unhappiness. For all you maga people who are so hard-headed about this, this is stupid. These Democrat people who've come over, they aren't Republican, they're Democrat, with a Republican label. They're RINOs. They need to go back to the left.

- Then, Ronald Reagan came along with his famous speech about "bring down that wall", and you can say the rest is history. No, Russia was never communist, but for many decades were pushing for that goal. They had a communist party in charge during that time, but had not achieved that goal. And they are capitalist now, not Socialist, they WERE socialist.

In the end, this is just some but the most obvious reasons why the USSR fell.