The year 1916 began in much the same vein as 1915 had passed. On 9 January, the last Allied troops were evacuated from the Gallipoli peninsula. The bold plan for defeating the Turks had backfired disastrously. Its political father, Winston Churchill, who had already resigned from the government over the initial failure of the Gallipoli campaign in May 1915, was by this time a battalion commander in France.

The war on the Western Front was characterised by particularly bloody and brutal stalemates in 1916. Between February and December, French forces repelled an intense and sustained German attack on the fortress of Verdun, an important staging post for invading armies on the road to Paris. Anglo-French forces launched a massive offensive of their own against German lines around the River Somme in July.

Neither attack achieved its objective. German troops failed to take Verdun, just as Anglo-French forces made only small gains in the Somme offensive. In both cases, the loss of life was horrific: over 300,000 men on the Somme by November, and in the region of 370,000 Allied and 350,000 German soldiers at Verdun. By the end of the Somme campaign, more than a million men had been killed: around 420,000 British and Dominion soldiers, over 200,000 French, and probably around 450,000 German.

The strains of the war showed on all sides. Britain, the only major combatant with a volunteer army, introduced conscription in early 1916. Depleted manpower resources forced governments throughout Europe to begin deploying women in various hitherto male-only jobs on the home front. Signs of popular disillusionment with the ongoing conflict, such as labour unrest and food riots, were increasingly common. Anti-war voices, from the Quaker-led No-Conscription Fellowship in Britain to the Bolshevik Party in Russia, gained influence.

Different countries sought different political solutions to the military impasse. Asquith was finally replaced as British prime minister in December 1916 by David Lloyd George. He rejected outright the German offer of peace negotiations made in the same month and called for the Allies to redouble their efforts against the Central Powers. In Russia, the war brought revolution in its wake. The bold successes of the Brusilov offensive in the summer of 1916 were short-lived. By Christmas, the Germans had counter-attacked successfully in Romania - which had joined the war against the Central Powers in August - and occupied Bucharest. Less than three months later, the tsarist regime collapsed.

Under the leadership of Woodrow Wilson, the United States had adopted a position of neutrality when war broke out in August 1914. However, as the conflict dragged on, voices within the American political establishment, such as former president Theodore Roosevelt, grew increasingly critical of its aloof 'pacifism'.

Germany's declaration of unrestricted submarine warfare in February 1917 and the subsequent torpedoing of numerous American ships finally forced Wilson to reassess his country's position. The USA declared war on Germany on 6 April - although the full impact of American intervention was not really felt until the following year.