True. Communism failed because it DOESN'T WORK. It fails every time because it ignores basic human nature.
These were some of the greatest men in the world.
True, if you define "greatest men in the world" as having the highest body counts in pursuit of power. Otherwise they were agents of Satan, in the purest sense.
You consider it a failure because it didn’t deliver what it promised. But what if they intended goal was a politburo with power over the people? Power over the means of production? Power over vast territory? Power over thought?