Vladmir Lenin: After the Bolsheviks seized power during the Russian Revolution of 1917, Lenin negotiated the Treaty of Brest-Litovsk. The treaty ended Russia's involvement in World War I, but on humiliating terms: Russia lost territory and nearly one-quarter of its population to the Central Powers.
Tsar Nicholas II: When Austria-Hungary declared war on Serbia, Russia's alliance with its Balkan neighbor forced it to enter the war against the Central Powers. The tsar assumed control of the Russian army, with disastrous results. In 1917, he was forced to abdicate, and he and his family were executed in 1918.
Georges Clemenceau : As prime minister of France from 1917 to 1920, Clemenceau worked to restore French morale and concentrate Allied military forces under Ferdinand Foch. He led the French delegation to the peace talks ending World War I, during which he insisted on harsh reparation payments and German disarmament.
Ferdinand Foch: Foch led French forces at the First Battle of the Marne, but was removed from command after the Battle of the Somme in 1916. In 1918, he was named Allied Supreme Commander, coordinating the war's final offensives. Foch was present at the armistice ending the war in November, 1918.
Marshall Philippe Pétain: Pétain became a national hero in France after his success at the Battle of Verdun during World War I. However, during World War II, Pétain headed the Vichy regime, a pro-German puppet government, and as a result has a mixed and deeply controversial legacy.
Winston Churchill, 1918: In 1911, Churchill became First Lord of the Admiralty. In this position, he worked to strengthen the British navy. He was pushed out of office after the disastrous 1915 Gallipoli campaign, in modern-day Turkey, which resulted in more than 250,000 Allied casualties.