in the 1919-1921 era the KPD- I'm NOT a Communist, for the record- was led by Rosa Luxemburg and Karl Liebknecht, both of whom were completely independent of the paranoid, conspiratorial mindset that produced Stalin and Stalinism.

Had Luxemburg and Liebknecht prevailed, the KPD would never have degenerated into Stalinism and the extreme right-wing militias would have been stopped before they could grow- No Stalin or Hitler choice would ever occur, because Stalinism and Naziism would not have existed- which means there would have been no Stalinists and Nazis to ally with each other later on.

The way to have stopped Naziism would have been to allow a prosperous and independently socialist Germany to come to birth in the 1920s. Nothing the centrists supported- and especially not the "both sides are equally bad, so let's just arrest the Left" strategy and the austerity economics- with the massive economic desperation they caused- combined with the unnecessarily punitive and vindictive terms imposed on Germany at Versailles- terms which sabotaged the newly created democratic German government of the 1920s, a government which should not have been punished for the war- a war which was equally the fault of every European empire- but rewarded for bringing down the Kaiser and therefore making it possible for the war to end.