A Walachian contingent, apparently Mircea's, aided the Servian tsar Lazar in his vain endeavour to resist the Turks at Kossovo (1389); later he allied himself with his former enemy Sigismund of Hungary against the Turkish sultan Bayezid I., who inflicted a crushing defeat on the allied armies at Nikopolis in 1396.
The death of Stephen Dushan, in 1356, had left his empire defenceless against the Hungarians, Turks and other enemies; and to win help from Bosnia the Servian tsar Lazar ceded to Tvrtko a large tract of territory, including the principality of Tribunia.
His youngest son Lazar succeeded him, but only for a few months.
In accordance with his choice, Lazar fell fighting at Kossovo, and was buried at Ravanitsa; his body being afterwards transferred,.
There is a legend that here the Servian tsar Lazar (1374-1389) was visited by an angel, who bade him choose between an earthly and a heavenly crown.
The Latin movement was first brought into Walachia by a certain George Lazar from across the mountains.
The historians Faustus of Byzant and Lazar of Pharp in the 5th century already attest the reverence with which their memory was invested.
After a few years of indecision and anarchy the Sabor met at Ipek in 1374 and elected Knez (count) Lazar Hrebelyanovich, a kinsman of Urosh, as ruler of the Serbs.