Murad captured Niš in 1386, perhaps forcing Lazar of Serbia to accept Ottoman vassalage soon afterward. While he pushed deeper into the north—central Balkans, Murad also had forces moving west along the ‘’Via Ingatia’’ into Macedonia, forcing vassal status on regional rulers who until that time had escaped that fate. One contingent reached the Albanian Adriatic coast in 1385. Another took and occupied Thessaloniki in 1387. The danger to the continued independence of the Balkan Christian states grew alarmingly apparent.

When Anatolian affairs forced Murad to leave the Balkans in 1387, his Serbian and Bulgarian vassals attempted to sever their ties to him. Lazar formed a coalition with Tvrtko I of Bosnia and Stratsimir of Vidin. After he refused an Ottoman demand that he live up to his vassal obligations, troops were dispatched against him. Lazar and Tvrtko met the Turks and defeated them at Plocnik, west of Niš. The victory by his fellow Christian princes encouraged Shishman to shed Ottoman vassalage and reassert Bulgarian independence.