Which crusade caused the sack of Constantinople in 1204?

The Fourth Crusade caused the sack of Constantinople in 1204. Instead of reaching its intended target in Egypt and then Jerusalem, the crusade was diverted into Byzantine politics and ultimately attacked Constantinople, the capital of the Christian Byzantine Empire.

The diversion began partly because the crusaders owed money to Venice for ships and supplies. Byzantine prince Alexios Angelos promised payment and political concessions in exchange for help restoring his father, Isaac II, to the imperial throne. After the crusaders intervened and the promised arrangements collapsed, tensions turned into open war.

Crusader and Venetian forces captured Constantinople in April 1204. They looted palaces, churches, monasteries, libraries, and monuments, and established the Latin Empire over much of Byzantine territory. The destruction shocked the Orthodox Christian world and deepened the division between the Roman Catholic and Eastern Orthodox churches.

The Third Crusade had been fought against Saladin after his capture of Jerusalem, while the Fifth and Sixth Crusades occurred later and pursued different objectives in Egypt and the eastern Mediterranean. The sack of Constantinople is therefore a defining event of the Fourth Crusade—and one of the most consequential episodes in the history of the Crusades.