The collapse of the Byzantine Empire was influenced by various factors, including military defeats, economic decline, and internal strife. Key events included the loss of territory during the 11th-century Crusades and the rise of powerful enemies, like the Ottoman Turks. The Fourth Crusade in 1204 led to the sack of Constantinople, severely weakening the empire. Additionally, economic issues such as trade competition and reliance on mercenaries strained resources. Internal political conflicts and corruption weakened central authority, leading to fragmentation. Ultimately, the fall of Constantinople in 1453 marked the definitive end of the Byzantine Empire, paving the way for Ottoman dominance in the region.