The Battle of Passchendale
Despite the Russian successes in 1916, by early 1917 Russian would find itself in the throws of a full-blown revolution that would sweep the Tsar from power and replace him with a new Soviet regime by the end of the year. German unrestricted submarine warfare was threatening to choke off supplies to the British home islands, and in France mutinous murmurs within the army were only silenced by promises that they would not have to conduct an attack for six months.
Faced with the prospect of a million new German troops freed up from the eastern front, and the danger of internal collapse in the west, in July 1917 the British would launch the last great set-piece battle of the war at Passchendale in Belgium in the hopes of ending the war immediately. Though the British did gain some ground early in the battle, the offensive ground to a halt when weather conditions turned.
The month of August saw the worst rains in thirty years. Situated as it is in the Low Countries, the water table at Passchendale was in places only a few feet below the surface, and it became saturated by the rains. The earth, churned by artillery, turned to a literal quagmire in which soldiers who stepped off duck boards laid over the ground could simply be swallowed up by the mud. The British commander, Douglas Haig, persisted all the same.
As the battle dragged on into the fall, the British gained support from Canadian forces, who renewed the offensive in October. The Canadians would manage to do in ten days what the British had failed to accomplish in three months, taking the ridges overlooking Passchendale. German general Ludendorf would later write that the defeat of Germany began at Passchendale, but they had not yet given up and a year of bloody fighting still remained.