section_path: Late Middle Ages/Collapse of Byzantium and rise of the Ottomans
section_name: Collapse of Byzantium and rise of the Ottomans
paragraph_text: Collapse of Byzantium and rise of the Ottomans
  
  Facing financial crises and threats from the west, the restored Byzantine Empire was unable to prevent Turkish expansion in Anatolia. Revolts by Catalan mercenaries and recurring civil wars further weakened the empire, allowing the Ottoman Turks to establish a strategic bridgehead at Gallipoli in 1354. Within a century, the Ottomans reduced the competing southeastern European kingdoms, principalities and lordships to tributary states. International coalitions, such as the crusades of Nicopolis (1396) and Varna (1444), could not stop their advance. The last Byzantine emperor, Constantine XI (r. 1449–53), died during the conquest of Constantinople by Sultan Mehmed II (r. 1451–81). Talented military commanders could repel individual Ottoman attacks but the Ottomans conquered almost all of the Balkans; Bulgaria was occupied in 1396, Serbia in 1459, Byzantine Greece in 1460, Bosnia in 1463, and the Albanian lords' resistance was broken by 1488. Ottoman rule was highly centralised, and sultans often appointed slaves to the highest offices. During the late 15th century, the sultans began murdering their brothers to avoid succession crises.