Why: Berlin was the capital city of Germany, a country that had started World War II, and the Allies wanted to capture this major city in order to bring the war to an end. Germany was the only country that opposed the Allies after Italy switched side. The Soviet Union, part of the Allies, had to capture Berlin in order to bring the war to a final end in Europe.
Significance: The Battle of Berlin is a key battle in World War II because it led to an unconditional surrender from Germany since Germany had lost it leader and a majority of it military force. After this decisive battle, the war was favoring the Allies as victors.