They were to fight the German army on land to free France. After the Dunkirk evacuation some years ago, this was the first time that the British army was on the ground to fight the German army. This was a dangerous situation for Hitler. Hitler had directed his army to focus on the Soviet Union.
There they were facing losses due to the cold they couldn’t defeat the Soviet Union completely. And now they were being attacked from the Western front as well. So Hitler decided that it was better to withdraw the army from the Eastern front, and to focus the counterattack on the Allied forces moving in from the West.
As soon as Hitler withdrew his army from the Soviet Union there was a major counterattack from the Soviets. Within 2 months, the Soviets regained around 600km of territory from Germany. Poland, Czechoslovakia, Hungary, and Romania were under the occupation of the Soviet Army.
On the other side, the Allied Forces landed in Southern France too. One after another, countries were being liberated. Hitler’s army was being thrown out. Yugoslavia threw out German troops on its own strength. Germany was being attacked from three sides.
Hitler planned his last major offensive. The Battle of Bulge. In the forest region of Ardennes, The German army intended to drive out the Allied forces. Before formally invading Germany Allied Forces carried out devastating aerial bombings on German cities.