German invasion of the USSR (Operation Barbarossa), What is the significance of this event?/What resulted from it?

Indeed,
the miscalculation in believing that Hitler could overrun the Soviet Union is where the greatest
result from the campaign exists.  I think that Hitler's desire to go after Russia, similar to
Napoleon, bogged him down so much that fighting on both fronts became nearly impossible. 
Another reason why it was significant was that the conflict displayed two similar leaders, once
aligned with one another, now actively against one another.  Stalin and Hitler were two leaders
cut from the same cloth and their conflict in the Eastern theatre was so intense because it
represented a similar magnitude of leadership seeking to overwhelm the other.  Both of these
dictators' attacking one another, allowed the other two of the "the big three" to
attack Hitler from the West and helped to ensure an Allied victory in
Europe.