In the story, German revolution happens in the 1930s (1930 according to wikipedia).
KPD at least partially takes the IOTL place of NSDAP.
Scenario for 1936: A popular front of socialists and communists takes power, right-wing forces attempts a military coup with results similar to the Kapp putsch, except this time it is the communists and not republicans who takes power.
Communists holds most industrial regions and soviet-union gives the most help, right-wingers are crushed or flee in exile.
France have a leftwing governement and Poland would face red army attack if attempting to invade Germany.
Austria/Italia/Hungarya/Poland/Romania forms some sort of military alliance.
Some anti-communist partisans remains in Germany but that only afford reinforce security apparatus, modeled on the NKVD.
Scenario for 1937-1949: Leftwing governement in France brokes down, instead there is a rightwing coalition taking power.
Germanic and CCCP assistance results in republicans winning the spanish civil war, Franco forms a governement-in-exile in Italia.
France & Britain pledge support to anti-communist coalition and start increasing dramatically their military production.
Against this encirclement, there is an even greater Madrid/Berlin/Moscow cooperation.
5-6 years after the German revolution, governement demand return of Austria to Germany, coalition refuses and war starts. Eastern coalition is far bigger than IOTL czecoslovakia, hence France & Britain cannot back down.
Within a few weeks Austria is integrated into Germany, within a few months Poland is crushed by the combined offensives of the red armies.
Within a year, anti-communist coalition is completely crushed despite French & British expedition forces.
Spain have invaded Portugal and is itself facing invasion form the French but the French are not that reluctant to attack and face much guerilla war and partisan warfare.
France is attacked throught Belgium (& perhapse Holland as well), battle is much more brutal as blitzkrieg have not quiet emerged as in OTL, France doesn´t surrender as easely as much of their forces where in Spain when attack occured.
Those forces fortify themself in southern France, using mountainous geography, for long time enought to evacuate to North Africa.
Communist forces are unchallenged in continental europe, a massive build-upp to the invasion of britain begins, britain itself is initially struck by bombing raids.
Later it becomes a battle for air superiority, with lesser ressources the RAF is finally defeated.
Submarines production kicks in, which causes tensions with the USA but not outright war yet.
Britain is defeated in India, Middle-east then North Africa before invasion of british isles themself is launched as Berlin-Moscow fears that the US will intervene and keep the war going.
There is a hard battle, with red armies struggling to get out of their beach heads.
British forces retreates to Scotland, then Irland.
Japan have been expanding its hold over Indochina and China, for years Japan have cooperated militarily with France & Britain, then with the USA. By the time invasion of britain starts, the USA starts secretely shipping US military forces to China and works on the atomic bombe is well on its way.
Question remain, would Berlin-Moscow alliance last? Or would europe be divided into two communist blocks?
PS: Found this thread while searching for "Iron Dream" topics.