Hitler got greedy.
If he stopped after taking France and left the Soviets alone he'd have been ok.
Stalin would have made a move...
The mistake was Barbarossa came a little to late, the Russians were highly disorganised after stalins purges which killed of most of the officer core, the Russians also hasn't ramped up production of the new weapons like the t34 tank...
that's why nazis made the move trying to preempt the organisation of the Russians ... Hitler and nazis were well aware that had the Russians gotten another year or two they would roll over Germany on man power and production which is what happened anyway.
The Germans got damn close, winter sealed the deal only 30 miles from Moscow.