To be honest I think it's next to impossible. I suppose maybe have Rosa Luxembourg emerge as leader of Germany around 1919 And Germany and the Soviet Union form a strong alliance. World War II starts just as it did in OTL with the main difference Germany has no interest in backstabbing Russia. France and Britain declare war on Germany after the invasion of Poland, which prompts Russia to declare war on Britain and France. France falls like in OTL, Spain is communist since Mussolini and Hitler aren't around to support Franco, And subsequently all of continental Europe becomes communist As Russia and Germany take over the continent. That is as far as I can go, I can't figure out a way to make Briton communist without involving sea mammals, And to be honest the scenario above is rife with problems. I doubt German Communists would really get along with Joseph Stalin, and I would predict a literal Sino-Soviet split to emerge. Also, Britain and France Were terrified of international communism, and in OTL they were very active in trying to crush the communist movement. So much so that they were willing to ignore Adolf Hitler until it was too late. A communist Germany and 1920 would probably prompt France and England to actually invade Germany. I suppose if France and Britain acting uncharacteristically and ignore this communist threat Until it was too late then maybe this scenario can work. But I'll be honest this stretches plausibility quite a bit And sorry, no way you can make the United States communist as well