<P> By the mid-1380s Murad's attention once again focused on the Balkans . With his Bulgarian vassal Shishman preoccupied by a war with Wallachian Voievod Dan I of Wallachia (ca . 1383 - 86), in 1385 Murad took Sofia, the last remaining Bulgarian possession south of the Balkan Mountains, opening the way toward strategically located Niš, the northern terminus of the important Vardar - Morava highway . </P> <P> Savra field battle was fought on 18 September 1385 between Ottoman and Serbian forces . The Ottomans were victorious and most of the local Serbian and Albanian lords became vassals . </P> <P> 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 . </P> <P> 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 . </P>

Who was driven out of the middle east under osman's leadership