The Germans invaded Soviet Union in what is known as operation Barbarossa which started in June 22, 1941. The initial assault by the Nazi was successful because the Soviet soldiers were taken by surprise and they withdrew, However, the Germans could not prevail in the war because as the Soviet Army withdrew, they destroyed anything that will be useful to the Nazi army and secondly, the winter came early that year which made the invasion by the Germans more difficult, their tanks broke down during the winter forcing them to withdraw. This was a significant point in the second world war because it marked the beginning of the defeat of the Nazi army.
Answer: German invasion of the Soviet Union succeeded at first because the Soviets were not prepared.
Explanation:
The Germans invasion of the Soviet Union was successful at first because the Germans prepared and the Soviet Union were not prepared. Before the invasion, the Germans had their troops near the Soviet Union border. Adolf Hitler had move about 3 million German troops and about 690,000 Axis soldiers to the borders of the Soviet Union. Their operations also included several aerial surveillance over Soviet territory some months before the attack.
The Soviet High Command got information about the proposed attack but didn't believe the Germans would attack since the Molotov–Ribbentrop Pact was recently signed and this led to a slow preparation by the Soviet.