Since the Allies landed in Normandy, the British and American armies (among affiliated Western Allied forces) had both moved swiftly and decisively to take western cities in France, and to move on to liberate Paris. By September 1944, Allied forces had reached the German border, but the subsequent failure of Operation Market Garden prevented a decisive breakthrough into the heart of Germany by the end of the year. In December, Hitler launched an unsuccessful offensive known as the Battle of the Bulge.