They know from their parents and grandparents. Source: I am rather in the parent category.

Yeah, all these sources pushing communism aren't telling them how the Bolsheviks killed everybody that knew how to do anything: farmers, lawyers, doctors because they were deemed part of the problem, probably because they were the only ones saying "this is a bad idea."

Then the soviets were back in the dark ages, and only got up to speed because of Germany fucking with them in WW2, and not accounting for the winter. So they were saved by the winter, and Stalin, under threat, threw everyone into the machine.

Millions of the workers were being killed - overworked to death - to get the Soviet war machine up to snuff in factories producing ammo, weapons, planes, whatever. No food, no water, just munitions to fight Germany, then to build bomb, then space flight, the. Collapse.

But, to be fair, all that stuff crippled the US too. In 1970, when everything started going tits up, that's when it caught up with us, and we're still paying the bill with ious to the Chinese. When those loans come to call, there will probably be another revolution, or at least war because some asshole is going to say "Look what China is doing to us."