The Russian Empire entered World War I with enthusiasm and patriotism as a member of the Allies, with the defense of their fellow Orthodox Slavs, the Serbs, as the main battle cry. In August 1914, the Russian army invaded Germany's province of East Prussia and occupied a significant portion of Austrian-controlled Galicia in support of the Serbs and their allies. However, military reversals and supply shortages among the civilian population, however, soon soured much of the population.
German control of the Baltic Sea and German-Ottoman control of the Black Sea severed Russia from most of its foreign supplies and potential markets. The Tsar was overthrown in February 1917, but the new provisional government continued the war. They, in turn, were deposed in October by the Bolshevik party who sued for peace with the Central Powers.