World War I saw the continent of Europe split into two major opposing alliances; the Allied Powers, primarily composed of the United Kingdom of Great Britain &amp; Ireland, the United States, France, the Russian Empire, Italy, Japan, Portugal, and the many aforementioned Balkan States such as Serbia and Montenegro; and the Central Powers, primarily composed of the German Empire, the Austro-Hungarian Empire, the Ottoman Empire and Bulgaria. Though Serbia was defeated in 1915, and Romania joined the Allied Powers in 1916, only to be defeated in 1917, none of the great powers were knocked out of the war until 1918. The 1917 February Revolution in Russia replaced the Monarchy with the Provisional Government, but continuing discontent with the cost of the war led to the October Revolution, the creation of the Soviet Socialist Republic, and the signing of the Treaty of Brest-Litovsk by the new government in March 1918, ending Russia's involvement in the war. One by one, the Central Powers quit: first Bulgaria (September 29), then the Ottoman Empire (October 31) and the Austro-Hungarian Empire (November 3). With its allies defeated, revolution at home, and the military no longer willing to fight, Kaiser Wilhelm abdicated on 9November and Germany signed an armistice on 11 November 1918, ending the war.