Твртко I
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.