Romania, which was situated between Austria-Hungary and Bulgaria, both members of the Central Powers, remained neutral until 1916. On August 27, Romania invaded Hungary through several passes in the Transylvanian Alps. This campaign met with some initial success, but the Central Powers quickly pushed back. By the end of January most of Romania, excepting part of Moldavia, was in the hands of the Central Powers. After Russia sought an armistice with Germany, there was nothing for Romania to do but surrender, signing an armistice with the Central Powers at Focsani on December 9, 1917. In the Treaty of Bucharest in 1918, Romania ceded a small amount of territory to Austria-Hungary and Bulgaria and accepted various economic penalties. It was allowed to retain Bessarabia, with which it had recently reunited. After the war, the defeated Central Powers were forced to return the territory acquired in the Treaty of Bucharest as well as hand over Transylvania to Romania.