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. 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. April 1917: the United States enters the war The United States was a major supplier of war materiel to the Allies but remained neutral in 1914; many opposed the idea of involvement in "foreign wars", while German Americans made up over 10% of the total population in 1913. 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