III. The Postclassical Period, 500–1500 > B. The Middle East and North Africa, 500–1500 > 2. The Muslim Middle East and North Africa, c. 945–1500 > d. The Ottoman Empire > 1. From Frontier Principality to Regional Power > 1362–89
  The Encyclopedia of World History.  2001.
SULTAN MURAD I. Under Orhan's son, the Ottomans extended their control into Thrace, Macedonia, Bulgaria, and Serbia, establishing the core of their empire in Europe. At this stage of expansion, their hold in these territories (which were known as Rumeli or Rumelia) was based in good part on suzerainty over tributary vassals rather than direct rule. Turkish populations were encouraged or forced to settle in the conquered lands, and fiefs (called timars) were granted to the army commanders, entitling them to the taxes on the land in return for military service and the administration of the population in their areas. Murad created the JANISSARIES (in Turkish, Yenicheri, or “New Force”), an infantry corps drawn from slaves originally captured in warfare. These troops developed into the principal fighting force of the Ottoman Empire.  1
Ottoman conquests in southern Bulgaria and Thrace. Adrianople (Edirne), the capital of Thrace, was captured and soon became the seat of government and the main base for further conquest in Europe.  2
Ottoman annexation of parts of the Anatolian principalities of Germiyan and Hamideli.  3
Ottoman conquest of Sofia.  4
Ottoman conquest of Nish in southern Serbia.  5
Ottoman conquest of the port of Salonika (Thessaloníki).  6
1389, June 15
BATTLE OF KOSOVO (See 1389 (Traditionally June 15)). The Ottomans defeated a large combined Serbian and Bosnian force in what was their first victory against a major European allied army. The success established their presence as the leading power in the Balkans south of the Danube. Murad was killed in the battle, but his son Bayezid, present on the scene, immediately assumed leadership.  7
SULTAN BAYEZID I, the energetic new ruler (known as Yildirim, or the Thunderbolt), inherited a fragile empire. The news of his father's death prompted the subjugated principalities in Anatolia as well as the Balkan vassals to assert themselves against Ottoman control, and Bayezid responded with a series of campaigns that brought much of Anatolia and the Balkans under direct Ottoman rule.  8
Although his efforts at empire building were dealt a serious setback by the onslaught of Timur-I Lang from the east (See 1394), Bayezid left an important mark on Ottoman state institutions. Most noteworthy was his promotion on a large scale of the practice (known as the devshirme) of levying Christian children to fill positions in the palace, administration, and the Janissary corps. These recruits, who were educated, converted to Islam, and then employed in official positions, provided the sultan with an elite group of loyal servants as well as a useful counterweight to the political power of the Turkish notables. Under Bayezid's successors, the recruitment of slaves for official service grew into one of the distinctive institutions of the Ottoman state.  9
Ottoman conquest of the Turkoman principalities of Saruhan, Aydin, Menteshe, Hamideli, and Germiyan, and the eastern territories of Karaman. Most of western and central Anatolia thus became Ottoman.  10
The Ottomans captured Skopje in Macedonia and annexed the Jandarid principality based in Kastamonu.  11
Ottoman annexation of most of Bulgaria, which had been a vassal state.  12
Ottoman conquest of parts of Albania.  13
The Encyclopedia of World History, Sixth edition. Peter N. Stearns, general editor. Copyright © 2001 by Houghton Mifflin Company. Maps by Mary Reilly, copyright 2001 by Houghton Mifflin Company. Published by Houghton Mifflin Company. All rights reserved.