Romania on 27 March. On 7 May 1918 Romania signed the Treaty of Bucharest with the Central Powers, which recognised Romanian sovereignty over Bessarabia in return for ceding control of passes in the Carpathian Mountains to Austria-Hungary and granting oil concessions to Germany. Although approved by Parliament, Ferdinand I refused to sign the treaty, hoping for an Allied victory; Romania re-entered the war on 10 November 1918 on the side of the Allies and the Treaty of Bucharest was formally annulled by the Armistice of 11 November 1918. Between 1914 and 1918, an estimated 400,000 to 600,000 ethnic Romanians served with the Austro-Hungarian army, of whom up to 150,000 were killed in action; total military and civilian deaths within contemporary Romanian borders are estimated at 748,000. Eastern Front Initial actions As previously agreed with France, Russian plans at the start of the war were to simultaneously advance into Austrian Galicia and East Prussia as soon as possible. Although their attack on Galicia was largely successful, and the invasions achieved their aim of forcing Germany to divert troops from the Western Front, the speed of mobilisation meant they did so without much of their heavy equipment and support functions. These weaknesses contributed to Russian defeats at Tannenberg and the Masurian Lakes in August and September 1914, forcing them to withdraw from East Prussia with heavy losses. By spring 1915, they had also retreated from Galicia, and the May 1915 Gorlice–Tarnów offensive then allowed the Central Powers to invade Russian-occupied Poland. On 5August, the loss of Warsaw forced the Russians to abandon their Polish territories. Despite the successful June 1916 Brusilov offensive against the Austrians in eastern Galicia, shortages of supplies, heavy losses and command failures prevented the Russians from fully exploiting their victory. However, it was one of the most significant and impactful offensives of the war, diverting German resources from Verdun, relieving Austro-Hungarian pressure on the Italians, and convincing Romania to enter the war on the side of the Allies on 27 August. It also fatally weakened both the Austrian and Russian armies, whose offensive capabilities were badly affected by their losses and increased the disillusionment with the war that ultimately led to the Russian revolutions. Meanwhile, unrest grew in Russia as the Tsar remained at the front, with the home front controlled by Empress Alexandra. Her increasingly incompetent rule and food shortages in urban areas led to widespread protests