No one.

Assuming a true free for all the USSR is best equipped to win the land war in Europe, their fast moving tank divisions backed up with infantry would quickly overwhelm the technologically superior, but numerically inferior German army. The fight for central and western Europe grinds on into a grizzly and protracted war eventually resulting the the Soviets taking France.

The USA takes note of this, and thus prepares to protect itself, bolstering it's navy and armed forces. The UK is relatively well prepared to defend itself from the Soviet threat thanks to a natural moat and the development of rapid deployment interception fighter techniques from RADAR as well as one of the most agile planes of the second world war.

Eventually stalemate falls, the Soviets struggling to push across the channel, the UK barely holding them off, and the USA making plans to annex the UK to act as a forward base. The UK development of the jet engine gives them an upper hand in defending their coast, as well as in delivering fire power against the Soviets. As a result the UK reannexes the traditionally English Normandy region in northern France. Seeing the USSR is on the back foot the USA take their chance to swipe in at Western Europe. Their attempts winning them the rest of France.

As dissent grows within the Soviet population, and with resources stretched keeping the UK and the USA at bay the USSR begins to crumble from within. Many millions starve to death. However Russia has the bomb. The early annexation of Western Europe has played into their hands in capturing scientists that would have been swept up in operation paperclip.

Now harrowed from nearly a decade of war Europe rises together to form a collective of people to prevent the likes of this ever happening again. The USA takes umbrage at this assuming that this European Union will use it's position to try to lever the USA out of being world leader. The USSR being a shadow of it's former glory, and with little to lose takes its chance while the USA and the EU are squabbling to launch a series of coordinated nuclear strikes against key targets. Eliminating capital cities in every European country as well as several major cities in the USA.

Awakening from the dust and radiation the Coalition of Mankind arises to create a one world state, to prevent this kind of thing from ever happening again.