The only way to make this feasible would be to hyper-wank the interwar revolutionary upheavals that followed the end of the First World War. So for example, if the Reds win the Finnish Civil War, the Hungarian Revolution, take power in Austria, and the Spartacist Uprising receives much more support leading to a civil war in Germany. In addition the Bolsheviks are more successful militarily in the Russian Civil War and are able to drive the last of the Whites out a few years earlier. In Poland, the threat of Communist regimes in Russia and Hungary, as well as the potential threat of a Red Germany to the east means that their army is divided, and they ultimately fall to a joint invasion. The Baltic states agree to align themselves to the socialist cause due to a mixture of diplomatic, economic, and military pressure. In Germany the French and British support the whites, whilst the Soviets and their allies support the Spartacists, effectively restarting the Great War. The fighting eventually leads to a stalemate in Germany and the Balkans, whilst Romania falls to a joint invasion by Soviet Russia, Ukraine, and Hungary after they tried to invade Transylvania.
The disparate revolutionary regimes agree to form a supranational union which eventually morphs into a unified state. This alt-USSR basically incorporates all the territory of Tsarist Russia, Austria-Hungary, and Romania, as well as a chunk of Germany (Eastern and Central Prussia, and Bavaria, and the surrounding areas).
The British and French governments, fearing socialist uprisings in their own territory, heavily suppress the trade unions and left-wing parties, driving them underground and radicalising them (which also has the effect of driving most of the remaining 2nd International parties in Europe into the revolutionary camp), and basically become right-wing military dictatorships. They then begin to establish an anti-Communist alliance across Europe and Asia, seeking to contain the revolution.
In Asia the Chinese Republic remains fairly left-wing and builds close ties with the alt-USSR, whilst Japan and its colonies are drawn into the anti-Communist alliance. The USA, not wanting to be drawn into foreign wars, and fearful of the
By the time the mid-20s roll around, the alt-USSR, under a left-Communist government seeking world revolution, spurred on by unrest in Europe and the colonies, as well as Japanese incursions into China, launches an all out attack against the anti-Communist Entente, with the hopes that one solid kick would bring it down. Unfortunately for them the anti-Communists aren't as hopeless as they fought and the Second World War begins.
The collapse in global trade brought about by the war, as well as the upsurge in revolutionary optimism results in a radical left-wing government coming to power in the USA, which leads to them offering economic and diplomatic support to the USSR, helping to turn the war in their favour, with them eventually joining to offer their naval support to invading Japan, Indonesia, Australia and New Zealand, and eventually Britain.
World Socialism is achieved by the mid-30s-40s. Thus endeth the Sovietwank.