The Fourth Crusade was called by Pope Innocent III in 1198.
The Fourth Crusade was intended to conquer Muslim-controlled Jerusalem by means of an invasion through Egypt.
However, a sequence of political events culminated in the Crusader army sacking the city of Constantinople.
The Crusaders of Western Europe invaded and sacked the Christian city of Constantinople. Enrico Dandolo was the first person to bring up the idea of passing through Constantinople.
The main objective of the Crusaders as to place Alexios on the Byzantine throne so that they could receive the rich payments he had promised them.
The Crusaders attacked the cities of Chalcedon and Chrysopolis. They won a cavalry skirmish in which they were outnumbered. They defeated 500 Byzantines with just 80 Frankish knights.
The Crusaders first traveled to Venice to discuss their plans. After their discussion, they went on to capturing Zara, Constantinople, and Thessalonica.
Zara and Constantinople were sacked. However, the Crusaders did not reach their main objective. The Byzantine Empire was weakened. The Fourth Crusades also led to the outbreak of the Nicaean-Latin wars and the Bulgarian-Latin wars.