The war on the Western Front had become one of attrition as 1917 drew to a close. The French Army was exhausted, having borne the brunt of the Allied effort and the trauma of Verdun. The British were beginning to suffer manpower shortages by early 1918, having increasingly taken over from the French in 1917.
Even the German Army was weakened, despite being able to concentrate entirely on the Western Front after the defeat of Russia. Its manpower was rapidly diminishing and its ally, Austria-Hungary, was crumbling. The cumulative effect of blockade was eroding morale at home. It was faced with a stark choice: make one major effort for victory or face the ever-increasing materiel power of the Allies and the arrival of US forces.
These conditions combined with the tactical and technological developments of three and a half years of war to initiate breakthrough. From March 1918, Germany concentrated her prime resources into a series of offensives, which gained unprecedented tactical successes but suffered from strategic failure. Over months of desperate fighting the Allies were pushed back, but not broken.
The summer saw a reversal of fortunes. With the British prominent the Allied armies deployed immense infantry and artillery firepower, tanks, aircraft and flexible tactics in a combined arms method that worked.
The increasingly weakened German Army was forced back to Mons, where it had all begun for the British Expeditionary Force in 1914. A defeated German high command agreed an armistice in November 1918.