structural:expansion, information:extraction
Russian Revolution and withdrawal

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 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 causing confusion and chaos, with frontline soldiers becoming increasingly demoralised.

Following the Tsar's abdication, Vladimir Lenin —with the help of the German government—was ushered 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, they acceded to the Treaty of Brest-Litovsk on 3 March 1918. The treaty ceded vast territories, including Finland, Estonia, Latvia, Lithuania, and parts of Poland and Ukraine to the Central Powers.

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. Under the terms of the treaty, Romania ceded territory to Austria-Hungary and Bulgaria and leased its oil reserves to Germany. However, the terms also included the Central Powers' recognition of the union of Bessarabia with Romania.