section_path: Progress of the war/Eastern Front/Romanian participation
section_name: Romanian participation
paragraph_text: Romanian participation
  
  Despite secretly agreeing to support the Triple Alliance in 1883, Romania increasingly found itself at odds with the Central Powers over their support for Bulgaria in the Balkan Wars and the status of ethnic Romanian communities in Hungarian -controlled Transylvania, which comprised an estimated 2.8 million of the 5.0 million population. With the ruling elite split into pro-German and pro-Entente factions, Romania remained neutral for two years while allowing Germany and Austria to transport military supplies and advisors across Romanian territory.
  
  In September 1914, Russia acknowledged Romanian rights to Austro-Hungarian territories including Transylvania and Banat, whose acquisition had widespread popular support, and Russian success against Austria led Romania to join the Entente in the August 1916 Treaty of Bucharest. Under the strategic plan known as Hypothesis Z, the Romanian army planned an offensive into Transylvania, while defending Southern Dobruja and Giurgiu against a possible Bulgarian counterattack. On 27 August 1916, they attacked Transylvania and occupied substantial parts of the province before being driven back by the recently formed German 9th Army, led by former Chief of Staff Erich von Falkenhayn. A combined German-Bulgarian-Turkish offensive captured Dobruja and Giurgiu, although the bulk of the Romanian army managed to escape encirclement and retreated to Bucharest, which surrendered to the Central Powers on 6 December 1916.
  
  In the summer of 1917, a Central Powers offensive 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 advancing 500 km. August von Mackensen could not plan for another offensive as he had to transfer troops to the Italian Front. Following the Russian revolution, Romania found itself alone on the Eastern Front and 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 leasing its oil wells to Germany. Although approved by Parliament, King Ferdinand I refused to sign it, hoping for an Allied victory in the west. 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.