What would have happened if Germans had created the atomic bomb first?
Just going alone with your “what if” here. Moscow would have been a glass parking lot. That’s where Hitler would have used the bomb, the demonstration of which might have caused the UK and the USA to back away. The Germans didn’t have a good delivery system, until maybe the V2. If a manned bomber had tried to get through to London, it would have been probably shot out of the sky. The Russians didn’t have the same kind of early warning that the UK did (radar), so laying one on Moscow would have been far easier, not to mention Hitler hated the Soviets far, far more then the Brits or Yanks.