Using the other Japanese WWII thread as a jumping off point, let's posit that for whatever reason, the American atomic bomb doesn't work as planned or Japan decides to keep fighting. An initial attempt at invasion is hampered by a typhoon, leaving the US to wait the Japanese out. The naval and air blockade tighten, the USSR invades from the north, and Japan starves to death.
So, we have a TL where the end of WWII is much bloodier than OTL. Millions more Japanese are dead, the Soviets control Hokkaido, and at the inaugural meeting of the UN the Soviets make a publicity stunt out of attempting to indict American generals for war crimes.
What happens next? Try to make it as dystopic as possible.
OK.
Israel is defeated in a prolonged war by its Arab neighbors; hundreds of thousands of Jews are forced to flee to the United States.
Stalin shuts down land routes to Berlin, in response, the United States sends a convoy towards Berlin to simply force the Soviets to make the decision to start a shooting war, and they do.
The United States attempts to use nuclear weapons to stop Soviet Land Superiority, but their weapons are too inaccurate and the Soviets were expecting such a campaign. Despite an ongoing Nuclear Campaign, the Soviets are able to smash US forces in Western Germany and drive all the way to Paris, creating a great Communist Crusade in Western Europe.
The Election of Robert Taft in 1948 on a platform of "No Entangling engagements abroad" leads to an exhausted United States giving up on Europe and Korea to the Soviet Union.
The United Kingdom never makes an economic recovery post WW2 because the United States refuses to compromise on its debts.
Stalin lives until 1964. With no reason to justify his actions, Europe has been directly annexed into the Soviet Union. This will be a sore spot for the Soviets for decades, but Stalin, and his successor, Beria, will greatly expand the gulag system to help the people of Europe discover the joys of communism through direct effort.
Chandra Bose emerges as the leader of Postwar India, his warped responses to Islamic Secession attempts leads him to endorse the "Shiva Solution" of expelling or killing the "Untouchables" of India.
The United States refuses to address the global situation, re-electing Taft in 1952 and returning towards a sleeping Giant Posture. The Soviet Union rules the world. Russification of Europe is a long, sordid affair that cumilates in the "Ethnocide" of Western Europe. Great buildings and works of time, like the Eiffel Tower, the Collessum and the Archepolis are razed in the name of a "New Era for Socialism". Tens of Millions die in the awful conditions of Soviet Gulags.
In 1981, the Soviet Union, under Beria's successor Mikhail Suslov, decides to use nuclear weapons to "Purify" the world. Left unchallenged for the last thirty years, the Soviet Nuclear Arsenal is designed to wipe out every bastion of Capitalism (and many places that arn't capitalist) as well. The USA is caught sleeping and their minimal nuclear response hurts only the fringes of Soviet Power. In triumph, the Soviets hold a vast parade through the ruins of what used to be Washington DC.
The Soviets now dominate the world. They paint the world red, and begin their great project of liberation from the tyranny of culture, religion, and unequal division of resources. The discipline of "BioSocialism" proves that some peoples are simply unfit to live in a Marxist state and these groups are simply destroyed.
Dominanted by Ideology and left with no objectives of their own, the Soviet Union survives until 2286, when it inadvertently releases its Biological Weapons and wipes out 99% of Humanity.