Actually, you're wrong, Jim--the Marxist/Communists beat everybody else out-check this:
Murder by Communism. Again, and, as you, I don't take pleasure in pointing it out. You are right, however, to point out that they differed from their predecessors only in scale--

Also right with "The vast majority of the countries that called themselves "Marxist" wouldn't know what Marxism was if they were belted over the head with a copy of 'Anti-Duhring'" You could say the same of countries that call themselves "Christian"--and insert just about any serious Christian writings from "The Imitation of Christ", to St. Francis, to St. Thomas Aquinas--in fact, most "Christian Nations" don't even get "Thou Shalt not Kill"--