There were, all in all, nine numbered Crusades in total (although technically, there were eleven), all of which was waged by Christian Europe against outsiders and non-believers.

Evidently, the Crusades were military campaigns designed to completely destroy all those who oppose them and to convert those who are willing. Much of the famed aggression was directed at Christianity’s main religious competitor, Islam and it’s followers, but the Crusades were also known to direct their attention to Jews, Pagans, Mongols, Greek Orthodox Christians, Russian Christians, Old Prussians and pretty much any group or individual who opposed the political influence of the reigning popes.

Constantinople, being a Eastern Orthodox territory, of course became a major target of the Crusades, though it would be interesting to note that the Fourth Crusade (1119-1204),

during which the warriors of Christianity’s cause had managed to capture the city, was originally focused on defeating Muslim Jerusalem by creeping up on it from Egypt. The Fourth Crusade undertook two different sieges, the second (1204) being far more successful than the first, thanks to the discontent of the citizens of Constantinople with their leader’s supposed cowardice. This success also led to the Latin Empire of Constantinople, which was ended by Michael VIII Palaelogus and his army of Niceans (1261); whose success was greatly aided by the Latin Empire’s weak defenses.