The following is a timeline of the events of World War I from 1917 to 1918.
Withdrawal and the Russian Revolution begins (March–November 1917)
By the end of 1916, Russian casualties totalled nearly five million killed, wounded or captured, with major urban areas affected by food shortages and high prices. In March 1917, Tsar Nicholas ordered the military to forcibly suppress a wave of strikes in Petrograd but the troops refused to fire on the crowds. Revolutionaries set up the Petrograd Soviet and fearing a left-wing takeover, the State Duma forced Nicholas to abdicate and established the Russian Provisional Government, which confirmed Russia's willingness to continue the war. However, the Petrograd Soviet refused to disband, creating competing power centres and caused confusion and chaos, with frontline soldiers becoming increasingly demoralised and unwilling to fight on.
In the summer of 1917, a Central Powers offensive began in Romania under the command of August von Mackensen to knock Romania out of the war, resulting in the battles of Oituz, Mărăști and Mărășești where up to 1,000,000 Central Powers troops were present. The battles lasted from 22 July to 3 September and eventually the Romanian army was victorious. August von Mackensen could not plan for another offensive as he had to transfer troops to the Italian Front.Keith Hitchins, Clarendon Press, 1994, Rumania 1866–1947, p. 269
Following the Tsar's abdication, Vladimir Lenin—with the help of the German government—was ushered by train from Switzerland into Russia on 16 April 1917. Discontent and the weaknesses of the Provisional Government led to a rise in the popularity of the Bolshevik Party, led by Lenin, which demanded an immediate end to the war. The Revolution of November was followed in December by an armistice and negotiations with Germany. At first, the Bolsheviks refused the German terms, but when German troops began marching across Ukraine unopposed, the new government acceded to the Treaty of Brest-Litovsk on 3March 1918. The treaty ceded vast territories, including Finland, Estonia, Latvia, Lithuania, parts of Poland and Ukraine to the Central Powers. Despite this enormous German success, the manpower required by the Germans to occupy the captured territory may have contributed to the failure of their Spring Offensive, and secured relatively little food or other materiel for the Central Powers war effort.
With the Russian Empire out of the war, Romania found itself alone on the Eastern Front and signed the Treaty of Bucharest with the Central Powers in May 1918, ending the state of war between Romania and the Central Powers. Under the terms of the treaty, Romania had to give territory to Austria-Hungary and Bulgaria, and lease its oil reserves to Germany. However, the terms also included the Central Powers recognition of the union of Bessarabia with Romania.Treaty of Bucharest with the Central Powers in May 1918R. J. Crampton, Eastern Europe in the twentieth century, Routledge, 1994, , pp. 24–25
United States enters the war (April 1917)
The United States was a major supplier of war materials to the Allies but remained neutral in 1914, in large part due to domestic opposition. The most significant factor in creating the support Wilson needed was the German submarine offensive, which not only cost American lives, but paralysed trade as ships were reluctant to put to sea. On 7May 1915, 128 Americans died when the British Passenger ship Lusitania was sunk by a German submarine. President Woodrow Wilson demanded an apology and warned the United States would not tolerate unrestricted submarine warfare, but refused to be drawn into the war. When more Americans died after the sinking of SS Arabic in August, Bethman-Hollweg ordered an end to such attacks. However, in response to British blockades, Germany resumed the use of unrestricted submarine warfare on 1 February 1917. On 24 February 1917, Wilson was presented with the Zimmermann Telegram; drafted in January by German Foreign Secretary Arthur Zimmermann, it was intercepted and decoded by British intelligence, who shared it with their American counterparts. Zimmermann hoped to exploit nationalist feelings in Mexico caused by American incursions during the Pancho Villa Expedition, promising support for a war against the US and help them recover territory lost from the Mexican–American War, although this offer was promptly rejected.
On 6 April 1917, Congress declared war on Germany as an "Associated Power" of the Allies. The United States Navy sent a battleship group to Scapa Flow to join the Grand Fleet and provided convoy escorts. In April 1917, the United States Army had fewer than 300,000 men, including National Guard units, compared to British and French armies of 4.1 and 8.3 million respectively. The Selective Service Act of 1917 drafted 2.8 million men, although training and equipping such numbers was a huge logistical challenge. By June 1918, over 667,000 members of the American Expeditionary Forces (AEF), had been transported to France, a figure which reached 2 million by the end of November. However, American tactical doctrine was still based on pre-1914 principles, a world away from the combined arms approach used by the French and British by 1918. US commanders were initially slow to accept such ideas, leading to heavy casualties and it was not until the last month of the war that these failings were rectified.
Despite his conviction Germany must be defeated, Wilson went to war to ensure the US played a leading role in shaping the peace, which meant preserving the AEF as a separate military force, rather than being absorbed into British or French units as his Allies wanted. He was strongly supported by AEF commander General John J. Pershing, a proponent of pre-1914 "open warfare" who considered the French and British emphasis on artillery as misguided and incompatible with American "offensive spirit". Much to the frustration of his Allies, who had suffered heavy losses in 1917, he insisted on retaining control of American troops and refused to commit them to the front line until able to operate as independent units. As a result, the first significant US involvement was the Meuse–Argonne offensive in late September 1918.
Nivelle Offensive and French Army mutinies (April–June 1917)
Verdun cost the French nearly 400,000 casualties, and the horrific conditions severely impacted morale, leading to a number of incidents of indiscipline. Although relatively minor, they reflected a belief among the rank and file that their sacrifices were not appreciated by their government or senior officers. Combatants on both sides claimed the battle was the most psychologically exhausting of the entire war; recognising this, Philippe Pétain frequently rotated divisions, a process known as the noria system. While this ensured units were withdrawn before their ability to fight was significantly eroded, it meant a high proportion of the French army was affected by the battle. By the beginning of 1917, morale was brittle, even in divisions with good combat records.
In December 1916, Robert Nivelle replaced Pétain as commander of French armies on the Western Front and began planning a spring attack in Champagne, part of a joint Franco-British operation. Nivelle claimed the capture of his main objective, the Chemin des Dames, would achieve a massive breakthrough and cost no more than 15,000 casualties. Poor security meant German intelligence was well informed on tactics and timetables, but despite this, when the attack began on 16 April the French made substantial gains, before being brought to a halt by the newly built and extremely strong defences of the Hindenburg Line. Nivelle persisted with frontal assaults and by 25 April the French had suffered nearly 135,000 casualties, including 30,000 dead, most incurred in the first two days.
Concurrent British attacks at Arras were more successful, although ultimately of little strategic value. Operating as a separate unit for the first time, the Canadian Corps capture of Vimy Ridge during the battle is viewed by many Canadians as a defining moment in creating a sense of national identity. Although Nivelle continued the offensive, on 3 May the 21st Division, which had been involved in some of the heaviest fighting at Verdun, refused orders to go into battle, initiating the French Army mutinies; within days, acts of "collective indiscipline" had spread to 54 divisions, while over 20,000 deserted. Unrest was almost entirely confined to the infantry, whose demands were largely non-political, including better economic support for families at home, and regular periods of leave, which Nivelle had ended.
Although the vast majority remained willing to defend their own lines, they refused to participate in offensive action, reflecting a complete breakdown of trust in the army leadership. Nivelle was removed from command on 15 May and replaced by Pétain, who resisted demands for drastic punishment and set about restoring morale by improving conditions. While exact figures are still debated, only 27 men were actually executed, with another 3,000 sentenced to periods of imprisonment; however, the psychological effects were long-lasting, one veteran commenting "Pétain has purified the unhealthy atmosphere...but they have ruined the heart of the French soldier".
In 1917, Emperor Charles I of Austria secretly attempted separate peace negotiations with Clemenceau, through his wife's brother Sixtus in Belgium as an intermediary, without the knowledge of Germany. Italy opposed the proposals. When the negotiations failed, his attempt was revealed to Germany, resulting in a diplomatic catastrophe.
Sinai and Palestine campaign (1917–1918)
In March and April 1917, at the First and Second Battles of Gaza, German and Ottoman forces stopped the advance of the Egyptian Expeditionary Force, which had begun in August 1916 at the Battle of Romani. At the end of October, the Sinai and Palestine campaign resumed, when General Edmund Allenby's XXth Corps, XXI Corps and Desert Mounted Corps won the Battle of Beersheba. Two Ottoman armies were defeated a few weeks later at the Battle of Mughar Ridge and, early in December, Jerusalem was captured following another Ottoman defeat at the Battle of Jerusalem. About this time, Friedrich Freiherr Kress von Kressenstein was relieved of his duties as the Eighth Army's commander, replaced by Djevad Pasha, and a few months later the commander of the Ottoman Army in Palestine, Erich von Falkenhayn, was replaced by Otto Liman von Sanders.