Why did hitler fail in the soviet union

The reason why Hitler failed at his invasion of the Soviet Union was because he forbade any form or tactical retreat, and because his method of attack known as Blitzkrieg went so fast even the supply lines couldn't keep up with it. When the forces of the Soviet Union prepared the siege against German troops stationed at Stalingrad, the general of those German troops at Stalingrad had desperately pleaded to Hitler for the permission to retreat, to no avail. Hitler's biggest problem in that scenario was the failure to think tactically, for if his troops ran away to fight another day, he might have won Operation Barbarossa. Second, the German Blitzkrieg method of armed warfare involving fast paced attacks reinforced by armored ground forces and air forces went so fast that by the time the Wehrmacht arrived at Stalingrad for the final push to Moscow, their supply lines were far behind them, and so they were out of useful supplies, which would cost them dearly at Stalingrad months later.

He signed a peace treaty with the Soviet Union in the beginnings of WWII but shortly after he attacked the Soviet Union.