Alow me to offer my theory on the collapse of the Soviet Union.
It didn't.
The Soviet Union realigned itself to function as a Communist state in the 21st century. No longer can a country by use of the gun force its people to be beholden to the state. In addition, no longer can a country force its ideology on people around the globe by use of expansionism.
The powers that be in Communist Russia came to the realization that it is easier to accomplish their goals peacefully where necessary and through peoples uprisings where necessary. Look at what is going on in the US by the left. Look at Venezuela and other nations in South America.
In addition, Russia needed hard cash. By opening up their country and allowing other countries to be sovereign, money started to flow back into the coffers of the same people that ruled by force. Many of those countries under the Soviet block became Democratic. However, the Communists no longer need to rule by gun. They now use the political and finacial system to achieve the same goals. They are grateful that American money is flowing freely in Eastern Europe. They still have politicians there who are Communist and who are winning elections.
To conclude, at one time Communism had defined borders. There was a fence around it with machine guns to keep people in. In the end the goal was to have a world like this. With technology, money, influence and power, the same can be accomplished just as easily at a rigged ballot box. There are no longer defined borders. There are only very wealthy people who want power and are using an ideology to achieve it.
To a Communist, everyone is equal. To a Communist leader, everyone is equal, but some are more equal than others.
Communism certainly is a mindset....could be argued that the mindset is a natural evolution from aristocracy/blood rule, to cash rule...though I suspect in the end the major players are reacting more to transnational corporate intrusion.