ww2 would probably still happen due to the allied powers demand of austerity. this time the war would be france, japan, italy, uk, usa, finland vs germany and ussr. i also bet they would not do their policy of appeasement at all with socialists
Einstein and his colleagues are still living in communist Germany, sorry.
Edit: On the Manhattan project:
This project came as the result of Albert Einstein learning that Germany was developing atomic weapons. Einstein relayed this critical information in a letter—known as the Einstein Letter—to President Franklin Roosevelt, and soon thereafter, the development of the atom bomb was elevated to the highest priority national security project.
source
Of course, you are correct in that there would’ve been a backlash by capitalist powers, but I don’t believe they would’ve dared to start a war with a unified Germany/USSR, possibly some other countries whose revolutions they might’ve helped along the way too. The US couldn’t be arsed to join the war until Pearl Harbor either, so…
