While the new Provisional Government vainly attempted to revive the Russian war effort, and American troops were withheld from battle by the commander of the American Expeditionary Force, General John Pershing, fresh attempts to break the deadlock on the Western Front were undertaken in the summer and autumn of 1917.

Despite the sobering experience of the Battle of the Somme and the misgivings of many politicians, the commander-in-chief of the British army in France, Douglas Haig, launched a renewed assault on the Ypres salient. At the Battle of Passchendaele (July-November 1917), the Allies gained more ground (4.5 miles) at less cost of life than at the Somme. Even so, some 250,000 French and probably a higher number of German soldiers lost their lives. The 'appalling casualty lists', as even Lloyd George conceded, brought into question the true worth of such 'great victories'.

A similar sense of false optimism was aroused by the first large-scale deployment of tanks on the Western Front, at the Battle of Cambrai in November 1917. Despite the creation in the same month of a Supreme War Council to co-ordinate Allied military affairs, it was the Central Powers that seemed closer to victory.

Austro-German forces finally made a breakthrough on the Italian front at the Battle of Caporetto in October 1917. Most importantly, the Bolshevik revolution ended Germany's 'war on two fronts'. Wanting no part in an 'imperialist' war, Soviet Russia signed an armistice with the Central Powers on 15 December 1917.

Russia's withdrawal from the war, confirmed in the Treaty of Brest-Litovsk on 3 March 1918, heralded a renewed German offensive on the Western Front. Its initial success during the spring of 1918 forced the Entente into desperate defensive measures. These included the appointment of General Foch as commander-in-chief of the Allied armies on the Western Front, and there was even talk of extending conscription to Ireland. It seemed that the Allies' best hope was to withstand the German onslaught and await the protracted entry of American forces into the conflict.

However, after the failure of the last great German push in mid-July 1918, the tide rapidly turned in the Allies' favour. Thanks to major tactical, command, organisational and technological improvements in the British and French armies, and the presence of nearly one million American troops now available in France, the Germans were pushed back towards their own defensive marker, the Hindenburg Line. The Battle of Amiens (8-11 August), in which the German army lost 27,000 men killed or captured, heralded a new, more mobile war on the Western Front.

The alliance of the Central Powers now collapsed on all fronts. In the autumn of 1918, as Bulgaria, Turkey, Austria and Germany sued for peace with the victorious Allies, thoughts turned from fighting the war to ending it.