What did Hitler form an alliance with the Soviet Union? Both countries were communist

Both countries spoke German

Hitler was afraid of fighting a war on two fronts

Hitler was afraid of the Soviet Army

Hitler was afraid of fighting a war on two fronts

but the real answer was that hitler wanted the soviets to break there forts in Belarus.

He was afraid of fighting a war on two fronts.

Explanation:

He had seen the disastrous effects of fighting on two fronts in WWI, which he served in. Though the Central Powers won considerable concession in the Treaty of Brest-Litovsk, they did not move those troops to the western front. Instead, they continued to station troops in the east, in an attempt to solidify their gains. The western front collapsed under joint Entente pressure, thus forcing Germany to sue for peace.