This year marked a turning point in the War. In Germany the British naval blockade created shortages of essential supplies. Military defeat helped produce a revolution in Russia. It was not clear at the time, but the impending Allied victory was becoming a reality.
Feb: Germany declared unrestricted submarine warfare. A Russian Revolution began.
March: The uprising against the Russian imperial government, resulted in the establishment of a provisional government. After a moderately successful 2-week drive on the Galician front, they lost much of the territory they had gained. On December 15 an armistice was signed between the Russian and Austro-German negotiators, and fighting ceased on the eastern front.
March: British seizure of Baghdad and occupation of Persia.
March-April: Germans retreated to Siegfried Line (ArrasSoissons) on Western Front.
April 6: The United States declared war on Germany. The United States had adopted a policy of strict neutrality. Past loyalty to France as well as the German invasion of neutral Belgium, however, resulted in the development of pro-Allied feelings in the United States.
The sinking of the Lusitania, the British passenger liner Arabic and the French channel steamer the Sussex with the loss of significant numbers of American lives, and of American ships by German submarines was the catalyst that aroused Americans to a warlike stance. By April 6, 1917, Congress approved a war resolution against Germany. War against Austria-Hungary was not declared until eight months later, on 7 December.
April 29: The exhausted French army began a mutiny. The mutiny was quelled and order restored by a change in French Marshall on May 15. The mutiny was concealed; French counterintelligence agencies completely blotted out all news of the mutiny.
June: The Allies began an invasion of Greece and on June 27 the Greek government declared war on all four Central Powers.
June 7: After a 17-day bombardment, British mines packed with 1.1 million pounds (500,000 kilograms) of high explosives tore a wide gap in the German lines on the Messines Ridge. Then, under cover of the British air force the Second Army successfully occupied Messines. Despite each side sustaining approximately 250,000 casualties, this victory encouraged British morale.
July 31 - 10 November: The Third Battle of Ypres began when the British attacked the Germans from the north-east.
The Allies had won temporary air superiority, but all surprise had been lost by the long preparation, and the German defence was well organised.
September 20: A series of minor assaults on narrow fronts began, and the British inched forward against determined counterattacks. For the first time, the Germans used mustard gas, that scorched and burned the British troops.
November 6: The offensive was concluded with the taking of Passchendaele Ridge and Passchendaele village by Canadian troops. The Ypres Salient had been deepened for about five miles, at great cost, approximately 240,000 British and 8,528 French casualties. German losses were estimated at 260,000. The Menin Gate (1927) is a memorial to British soldiers lost in these battles to capture the Passchendaele ridge.
November 20-December 3: The Battle of Cambrai was the first major tank assault in military history, during which the British opened the attack with a raid by nearly 400 tanks. But for lack of reserves, the British might have achieved a breakthrough. As it was, the British drove a five mile salient into the German lines. German counterattacks, however, compelled the British to yield most of the newly won ground.
December: Jerusalem taken by British forces under Allenby.