Have Communism start and lose WW II
After the end of the war communist parties became more popular in almost all liberated countries because of the role communists played in the resistance movement.
If the invader was communist instead of fascist/nazi would the same happen with fascist parties?
Hitler killed in the 1923 putsch. Weimar goes authoritarian nationalist in the Depression, copying Mussolini for a fascist flavor.
By 1940 the USSR has the largest modern army in the world, and decides to use it, invading Finland, Poland, Romania. Germany, Italy, and the Western Allies form an anti-Soviet alliance.
But they are underarmed and unprepared; Soviet forces reach Istanbul, Vienna and Berlin. Then the Allies rally; Soviet forces are overextended and politicized. Japan joins the USSR, but bogs down trying to seize SE Asia. German advisors pep up China.
The Allies push the Soviets back, with Germany as the point of the spear, but the others adding a lot of muscle. Moscow falls in 1943; Japan makes terms a month later.
German/Italian style regimes come to power throughout eastern Europe; Chiang consolidates China under fascism.
As Britain leaves India, Moslem fanatics assassinate Gandhi and Nehru. Bose seizes control, and enacts a militant Hindutva regime that is effectively fascist.
Fascist movements gain power in Brazil and Argentina.
