Excerpts from Books and Wikipedia
"When the Crusaders gathered in Venice in 1202, it transpired that there were too few of them, and they could not pay the agreed bill. Instead, they agreed to help Venice by taking Zara, Dalmatia--a rich source of wood for Venetian galleys. Pope Innocent protested, but worse was to come. In 1204, the Crusaders arrived in Constantinople, where relations with the Byzantines quickly soured; the city was taken for the first time in its history, and was brutally sacked. A new Latin Empire of the East was proclaimed under a new emperor, Baldwin of Flanders, while Venice was awarded nearly half the city, numerous Mediterranean islands, and other territories. Although the Byzantine emperors relocated to Byzantine Nicaea, the Fourth Crusade marked the end of the Byzantine Empire as a true power . . ." [Smithsonian, p. 140]