The Byzantine Empire
 1265

The Fourth Crusade (1202–04) instigated by Pope Innocent III recruited a considerable force of knights, mainly from France and Italy, who were to sail from Venice to Jerusalem. Due to financial difficulties they instead recaptured Hungarian Zara (Zadar) in Croatia for the Venetians and then sailed on to Consantinople, where they overthrew the ruling Greek Orthodox regime and sacked the city, conducting an infamous campaign of violence and looting. The crusaders proceeded to create a Latin Empire of feudal states in Thrace and Bythinia with subsidiary seats of power centred on Nicaea, Epirus in northwestern Greece and Trebizond on the Black Sea. These events greatly amplified the 11th-century schism between the eastern and western branches of the Christian church and sparked war with the Bulgarians, who in 1230 won an important battle at Klokonitsa and went on to capture Thessalonica. In April 1182 the Greek population of Constantinople rose up against the intruding ‘Latins’, who were largely massacred or forced to flee. In 1261 the Greek Laskarid and Paliologos Dynasties ruling Nicaea retook control of Constantinople and restored the Orthodox Byzantine Empire. However, it was now greatly weakened and soon became prey to advances by the Serbs in the west and the Turks in the east.