welcomed Hussite refugees (founders of Ciuburciu and, probably, Huși). The principality of Moldavia covered the entire geographic region of Moldavia. In various periods, various other territories were politically connected with the Moldavian principality. This is the case of the province of Pokuttya, the fiefdoms of Cetatea de Baltă and Ciceu (both in Transylvania) or, at a later date, the territories between the Dniester and the Bug rivers. Petru II profited from the end of the Hungarian-Polish union and moved the country closer to the Jagiellon realm, becoming a vassal of Władysław II on September 26, 1387. This gesture was to have unexpected consequences: Petru supplied the Polish ruler with funds needed in the war against the Teutonic Knights, and was granted control over Pokuttya until the debt was to be repaid; as this is not recorded to have been carried out, the region became disputed by the two states, until it was lost by Moldavia in the Battle of Obertyn (1531). Prince Petru also expanded his rule southwards to the Danube Delta. His brother Roman I conquered the Hungarian-ruled Cetatea Albă in 1392, giving Moldavia an outlet to the Black Sea, before being toppled from the throne for supporting Fyodor Koriatovych in his conflict with Vytautas the Great of Lithuania. Under Stephen I, growing Polish influence was challenged by Sigismund of Hungary, whose expedition was defeated at Ghindăoani in 1385; however, Stephen disappeared in mysterious circumstances. Although Alexander I was brought to the throne in 1400 by the Hungarians (with assistance from Mircea I of Wallachia), he shifted his allegiances towards Poland (notably engaging Moldavian forces on the Polish side in the Battle of Grunwald and the Siege of Marienburg), and placed his own choice of rulers in Wallachia. His reign was one of the most successful in Moldavia's history, but also saw the very first confrontation with the Ottoman Turks at Cetatea Albă in 1420, and later even a conflict with the Poles. A deep crisis was to follow Alexandru's long reign, with his successors battling each other in a succession of wars that divided the country until the murder of Bogdan II and the ascension of Petru III Aron in 1451. Nevertheless, Moldavia was subject to further Hungarian interventions after that moment, as Matthias Corvinus deposed Aron and backed Alexăndrel to the throne in Suceava. Petru Aron's rule also signified the beginning of Moldavia's Ottoman Empire allegiance, as