A communist world state is impossible. A majority communist world is very unlilkely due to the reactions and red scares. If both the USSR and Germany have successful revolutions, the Entente will become anti-communist in response. Geopolitics work like that.
However, we can play a little with that. Assuming a longer, bloodier WWI (a dystopic scenario on itself) that ends in a stalemate, and both Germany and the USSR succeeding in revolution. France and Italy might fall to Communism after feeling betrayed from the war. or at least a left wing version. Help from the Germans would be seen as treacherous after such a war, but let's assume local communists manage to rise to power. That's at least 4 great powers; and Spain, Turkey and others may join; Spain had a large left wing movement, and Turkey had cordial relations with the USSR from what I've read. China and India will have their own local movements as OTL
The UK and US (also Japan and other nations) at this point will become extremely right-wing in fear of the Communist tide. However, with Europe controlled by various left wing regimes (of what sort will define the scenario; but it is unlikely that Germans, French and Russians will have the same interests) a world-wide depression can start. And then, it's only a matter of lighting the fuse in Britain and the US. Whetever the socialists/communist succeed by rifle or ballot will define the future: either there will be a US/UK anti-communist alliance or they will fall to the red tide too.
By then, the world will be not be controlled by a single communist state, but virtually all great powers will have communist or left wing goverments of a sort. Other nations will try to either become more left wing to fit with the new world order, or fall into reactionary right-wing dictatorships.