What does China show? China became Communist in 1949 after Jiang pissed off a bunch of people and alienated the peasants by supporting the warlords. The only imperialist power 'watching over it' at that point was a US occupied puppet. The specter of Western imperialists threatening China was brushed aside by the very real threat of the Japanese in the 1930s. Persia, on the other hand, had the Russians and British to deal with at that point.
Which only shows that Marx was wrong about his whole "The Workers will rise!" spiel.
Marx was wrong for assuming a revolution to first occur in a place like Germany, where it was designed for. Ironically, it occurred in places that Communists would come to be called the worst, like Russia. Whether they would've worked better in places like Germany first is a debate for another time.
What China shows is a country with little to no industrialization(even less than Russia) can still experience a Communist revolt.
Now, Persia? Well, okay, it would require the Imperialist powers to be distracted, but again, that isn't impossible. In this situation, Russia can't intervene, having experienced a civil war, and also will have to reform, as even the Czars will realize at this point that the current system can't be continued.
So, that leaves GB, which while nothing to scoff at, isn't as bad as BOTH Russia and GB.