At the and of 1944 the Soviet and Allied armies were closing in on Germany's borders. With Germany lacking both human and material resources as well as being subjected massive aerial bombardments, The German command decided to focus it's efforts on driving the Allies out of Europe so that they could turn all of their energies on the Soviet Union.
The Allies were fielding 63 divisions, about 10,000 tanks and 8,000 aircraft. Germany could only master 1.5 times of fewer troops,900 tanks and 800 aircraft. The Germans were counting on three factors for success,Surprise, bad weather that would keep planes grounded, and the technical superiority of their tanks. They were also counting on being able to capture Allied fuel supplies to make up for their on deficit.
The German offensive began on December 16th and  caught the Allies completely off-guard. American defenses were breached quickly and multiple German commando groups and elite tank forces rushed deep into allied territory. Although plans to smash the enemy quickly and capture their supplies didn't work, the German offensive continued. Only the improving weather and subsequent allied air raids were able to stop the German offensive after it had covered a territory 80 km wide and 100 km deep. The German offensive on the Saar had also begun, aimed against the 7th American army. The Allied high command was baffled and they even decided to move the troop back. The British government asked the Soviet union to speed up the offensive on the Eastern front which then caused the Germans to cease active operations along the western front.

Despite the fact that the Ardennes offensive didn't achieves, it postponed the planed Allied offensive and allowed the German command to prepare the defenses in Berlin and fight on till the end of 1945.