The Republic of Venice was, at the time of of the Fourth Crusade, one of the most well-respected polities in the Mediterranean. During the third crusade, the Doge Mastropietro had carefully assessed the wealth of all leading families and decreed a forcible loan to be made to the state in order to construct ships to be put at the disposal of the crusading armies. Mastropietro's predecessor, Sebastiano Ziani, had acted as an intermediary between the Lombard Cities and Emperor Frederick Barbarossa after a lengthy series of wars in Northern Italy. The internal institutions in Venice, which included elections held in the Great Counci to nominate legislators in the Senate and the High Judges called the Quarantia, as well as the chief executive, the Doge, generated stability and consistency in foreign as well as domestic policy that few other states could reproduce.

By contrast, in 1200 Western Europe was rudderless. The King of Sicily was a five year old boy in the care of Pope Innocent III. In Germany, Otto of Brunswick was in open war against Philip of Swabia for the title of Kaiser. France, although ruled by the energetic Philip Augustus, was split between the Capetians and the Angevins, who were themselves coping with the death of Richard Lionheart and his successor John, whose epithet "Lackland" didn't exactly promise effective rule. In the east, Emperor Isaac II, after ten years of internal strife, had been dethroned by his brother, who had gained the support of the nobility through favors which in addition to his own incompetence made for extremely ineffective rule.

Given these conditions, the Fourth Crusade was fundamentally run by lesser princes and nobles, and rather haphazardly at that. The Republic, ruled at this time by Enrico Dandolo, although picked by the Crusade's commanders as the starting point of the expedition, wasn't as enthusiastic as it had been during the previous crusade the last decade, and would not put up the money to outfit the ships necessary. A compromise was reached: the crusaders would first stop in the Dalmatian city of Zara, a Venetian dominion which had recently rebelled against the Republic's authority, fight to re-instate Venetian rule, and in return the Venetians would ship them to their final destination.

Pope Innocent was furious, and excommunicated the Venetians for having used a crusading army for their own purposes. However, this had little effect on the crusaders, or the rest of Europe for that matter! Indeed, a further change of plan took place once Zara was retaken. Alexius, the son of the deposed Byzantine Emperor Isaac, had managed to escape from the prison where he was held and seek refuge in the court of his cousin, Philip of Swabia. Philip, who himself needed to strengthen his claim on the German throne, took up the guise of a seasoned statesman and proposed a further redirection of the crusade: the expedition would re-instate Alexius on the throne, who promised to finance the remainder of the expedition and provide ten thousand additional soldiers, in addition to promising to maintain five hundred knights to remain in the Holy Land after the conquest. An offer too good to pass up!

Of course, once Constantinople was taken and Alexius placed on the throne, the utter depletion of the Byzantine coffers made keeping such promises impossible, leading the crusaders to conclude that sacking the city was the best way to obtain that which was owed them. The Venetians under Dandolo for their part didn't do much to encourage cooperation, refusing to set sail for the Holy Land until Alexius fulfilled the promises he couldn't keep. However, even if Dandolo is recognized as the driving force behind the sack, he never held an official position beyond that of Doge of Venice. The leader of the expedition was one Boniface of Monferrat, although Dandolo undermined him at every turn and after the sack single-handedly elevated Baldwin of Flanders as the new Emperor. But under Baldwin the Byzantine Empire would be re-organized according to Western European feudal customs, it truly was a "Latin Empire," and the Venetian involvement, although significant and decisive, was fundamentally behind the scenes.

Sure, the Venetians expanded their own colonial empire in the Aegean and were the primary beneficiaries of the reorganized east. However, there was little sympathy in the west for the Empire to begin with. The Byzantines had even been accused multiple times of betraying the cause of the crusaders over the past century, and had long since stopped being an important player in Europe. In the end, through Sack of Constantinople the Venetians were able to enrich themselves while bothering no-one. Even Pope Innocent, the only one against the redirection of the crusade, changed his mind once he figured he would be able to unite the Eastern and Western Churches thanks to the reorganization of the Empire.