[Alex Murphy]

The Fourth Crusade (1201-1204) ran aground when it was seduced into a web of Byzantine politics, which the Westerners never fully understood. They had made a detour to Constantinople to support an imperial claimant who promised great rewards and support for the Holy Land. Yet once he was on the throne of the Caesars, their benefactor found that he could not pay what he had promised. Thus betrayed by their Greek friends, in 1204 the Crusaders attacked, captured, and brutally sacked Constantinople, the greatest Christian city in the world. Pope Innocent III, who had previously excommunicated the entire Crusade, strongly denounced the Crusaders. But there was little else he could do. The tragic events of 1204 closed an iron door between Roman Catholic and Greek Orthodox, a door that even today Pope John Paul II has been unable to reopen. It is a terrible irony that the Crusades, which were a direct result of the Catholic desire to rescue the Orthodox people, drove the two further—and perhaps irrevocably—apart.

Ping for later.

[Steve Van Doorn]

said, "Thus betrayed by their Greek friends, in 1204 the Crusaders attacked, captured, and brutally sacked Constantinople"

The rightful king was forced out of power the crusaders attempted to put him back into power that is why they attacked.

[Steve Van Doorn]

I would suggest watching this:
Why the Fourth Crusade Attacked Constantinople