The Eastern Front of World War 1 saw highly mobile warfare but also immense loss of life, with over 2.5 million Russian soldiers killed, captured, or wounded by 1915. Germany and Austria-Hungary were later joined by Bulgaria in attacking and eliminating Serbia from the war in late 1915. The Russian Revolution in 1917 and the subsequent Treaty of Brest-Litovsk signed by Vladimir Lenin removed Russia from fighting as a combatant nation, granting territory to the Central Powers.