In the fourteenth century, the Ottoman Turks expanded their empire from Anatolia to the Balkans. They crossed the Bosporus in 1352 and crushed the Serbs at Kosovo Polje, in the south of modern- day Yugoslavia, in 1389. Tradition holds that Walachia's Prince Mircea the Old (1386-1418) sent his forces to Kosovo to fight beside the Serbs; soon after the battle Sultan Bayezid marched on Walachia and imprisoned Mircea until he pledged to pay tribute. After a failed attempt to break the sultan's grip, Mircea fled to Transylvania and enlisted his forces in a crusade called by Hungary's King Sigismund. The campaign ended miserably: the Turks routed Sigismund's forces in 1396 at Nicopolis in present-day Bulgaria, and Mircea and his men were lucky to escape across the Danube. In 1402 Walachia gained a respite from Ottoman pressure as the Mongol leader Tamerlane attacked the Ottomans from the east, killed the sultan, and sparked a civil war. When peace returned, the Ottomans renewed their assault on the Balkans. In 1417 Mircea capitulated to Sultan Mehmed I and agreed to pay an annual tribute and surrender territory; in return the sultan allowed Walachia to remain a principality and to retain the Eastern Orthodox faith.
After Mircea's death in 1418, Walachia and Moldavia slid into decline. Succession struggles, Polish and Hungarian intrigues, and corruption produced a parade of eleven princes in twenty-five years and weakened the principalities as the Ottoman threat waxed. In 1444 the Ottomans routed European forces at Varna in contemporary Bulgaria. When Constantinople succumbed in 1453, the Ottomans cut off Genoese and Venetian galleys from Black Sea ports, trade ceased, and the Romanian principalities' isolation deepened. At this time of near desperation, a Magyarized Romanian from Transylvania, János Hunyadi, became regent of Hungary. Hunyadi, a hero of the Ottoman wars, mobilized Hungary against the Turks, equipping a mercenary army funded by the first tax ever levied on Hungary's nobles. He scored a resounding victory over the Turks before Belgrade in 1456, but died of plague soon after the battle.
In one of his final acts, Hunyadi installed Vlad Tepes (1456-62) on Walachia's throne. Vlad took abnormal pleasure in inflicting torture and watching his victims writhe in agony. He also hated the Turks and defied the sultan by refusing to pay tribute. In 1461 Hamsa Pasha tried to lure Vlad into a trap, but the Walachian prince discovered the deception, captured Hamsa and his men, impaled them on wooden stakes, and abandoned them. Sultan Mohammed later invaded Walachia and drove Vlad into exile in Hungary. Although Vlad eventually returned to Walachia, he died shortly thereafter, and Walachia's resistance to the Ottomans softened.