(June 15, 1389), battle fought at Kosovo Polje (“Field of the Blackbirds”), Serbia, between the armies of the Serbian prince Lazar and the Turkish forces of the Ottoman (Ottoman Empire) sultan Murad I (reigned 1360–89). The battle ended in a Turkish victory, the collapse of Serbia, and the complete encirclement of the crumbling Byzantine Empire by Turkish armies.

Murad captured many fortified places near Constantinople (now Istanbul) and used internal troubles in Byzantium and the Slavic states to extend Turkish conquests in the Balkan peninsula. Moving into Serbia, he marched as far as Kosovo, where he met Lazar's army.

At first, victory appeared to be on the side of the Serbs when the sultan was killed by a Serbian noble, Milosh Obilic (or Kobilic), who made his way into the Turkish camp on the pretext of being a deserter and forced his way into the sultan's tent and stabbed him with a poisoned dagger. The confusion that followed was quickly quelled by Bayezid (Bayezid I), Murad's son, who succeeded in surrounding the Serbs and inflicting a crushing defeat on their army. Lazar was taken prisoner and executed; the Serbs were forced to pay tribute to the Turks and promised to do military service in the sultan's army.

(October 17–20, 1448), battle between forces of the Ottoman Empire and a Hungarian-Walachian coalition led by the Hungarian commander János Hunyadi (Hunyadi, János) at Kosovo, Serbia. The Ottomans won a decisive victory and thereby halted the last major effort by Christian Crusaders to free the Balkans from Ottoman rule and to relieve Constantinople (Istanbul).

Following an Ottoman victory over the Crusaders at Varna (Varna, Battle of) (1444), the Ottoman sultan Murad II invaded the Morea (the Peloponnese) in 1446 and compelled its Greek rulers to be his vassals. Murad then turned against the Albanian leader Skanderbeg, who resisted the Ottomans and was assisted by forces of the pope and of the king of Hungary. In 1448 Hunyadi led an army of Crusaders across the Danube to join forces with Skanderbeg, but he suffered a crushing defeat at Kosovo. That victory did not lead to the conquest of Albania, but it strengthened the Ottoman position on the Danubian frontier.