World War 1
Germany was wracked by communist revolts in 1919 (but because they weren't Russian backed, they failed miserably) - which ended with Rosa Luxembourg and Karl Liebknecht being shot in a Freikorps prison.
In 1924, the NSDAP under Adolf Hitler rose to power after a brief civil war. He then began forging alliances with Italy and Japan. His skillful diplomacy with Spain helped end military and economic restrictions after WW1.
With the Russian Federation/Soviet Union less eager to co-operate with the Germans and hence no Rapallo or Berlin treaties like OTL, they turned to Fascist Italy and Imperial Japan, which gave them the leeway to test new tanks.