Excerpts from Books and Wikipedia
"The Fourth Crusade, summoned by Pope Innocent III, was not intended to travel to Constantinople. The crusaders had assembled at Venice in June 1202 to attack the Ayyubid dynasty in Egypt, which controlled Jerusalem and most of Syria, but they were unable to raise the money to pay for a fleet. Duped by the Venetians into attacking the port of Zara in Croatia for a share of the booty, they joined the Venetian army in attacking the city and restoring Emperor Alexius IV to the throne. But Alexius did not pay the reward, and when he was murdered six months later, the crusaders attacked the city again. For three days they ransacked Constantinople, venting their anger on the Greeks, whom they believed had betrayed them. . . . The sack of Constantinople permanently embittered relations between the Catholic West and the Orthodox East. It also completely destroyed the credibility of the crusading ideal" [1001 Days] The sacking of Zadar (Zara) occurred in 1202. Constantinople was sacked in 1204. [Wikipedia: Timeline of Middle Ages]