Why were the Soviets the first Allies to enter Berlin?

Fighting east of Germany, where the Soviets were, was not as fierce as the fighting west of Germany, where the Americans were.

The Germans believed they still had an alliance with the Soviets, and did not put enough defenses in the east.

The Americans had agreed to let the Soviets enter Berlin first to avenge the German invasion of the Soviet Union.

Stalin wanted to claim Germany as a Soviet territory, and forced his armies to reach Berlin first so he could do so.