The Fourth Crusade was called by Pope Innocent III with the intended goal of attacking Egypt, the center of Muslim power.

The crusaders contracted with Venice to provide sea transport, but they were unable to pay the full amount.

To pay off their debt, the Venetians persuaded the crusaders to first attack and capture the rival Christian port of Zara.

The crusade was then diverted further when an exiled Byzantine prince, Alexios Angelos, promised the crusaders immense rewards if they helped him take the throne in Constantinople.

The crusaders successfully installed Alexios as co-emperor, but he was unable to pay what he had promised.

Tensions escalated, leading the crusaders to attack and brutally sack the city of Constantinople, the capital of the Byzantine Empire, in 1204.

The sack of the world's greatest Christian city by a crusader army was a catastrophic event.

The crusaders established a 'Latin Empire' in Constantinople, which lasted for about 60 years.

The Fourth Crusade never reached the Holy Land.

It dealt a fatal blow to the Byzantine Empire and created a permanent schism between the Catholic and Orthodox churches.