The problem Crusade solves

The diversion of the Fourth Crusade from the Holy Land to attack, capture, and pillage the Byzantine city of Constantinople divided and dissipated the efforts of the Christians to maintain the war against the Muslims. It is widely regarded as a shocking betrayal of principles out of greed.

The Fourth Crusade was corrupted from its purpose early on. In order to repay Venice for shipping most of the crusaders eastward, they were obliged to seize Zara on the Adriatic from Christian Hungary on Venice’s behalf. Meanwhile exiled Byzantine prince Alexius offered a cash reward if he were put on the Byzantine throne.

The crusaders, therefore, sailed to Constantinople and in July 1203 set up Alexius as emperor. In February 1204 the new emperor was murdered and replaced by courtier Alexius Ducas, who told the crusaders to leave. The crusaders responded by laying siege to Constantinople. A first assault on the city’s defences was repelled with heavy losses, but on 12 April the crusaders were successful. Men swarmed up the masts of ships and scrambled across catwalks to reach the tops of the city walls. Other ships landed men on the shoreline to hack at a bricked-up gateway with picks and shovels. When a hole was broken through, Aleaumes of Clari crawled in to find the street beyond almost deserted. Hundreds of crusaders came through the enlarged hole, fought their way to the main gate, and opened it to their comrades. For three days the army pillaged at will, and then the nobles imposed order and began a more systematic looting of the greatest city in Christendom. The crusader nobleman Baldwin of Flanders was set up as emperor, but most Byzantines refused to recognize him, and the empire fragmented into four quarrelling states.

Challenges I ran into

Losses: Crusader, unknown of 20,000; Byzantine, unknown of 30,000, plus unknown civilian losses.