"The Entry of the Crusaders into Constantinople" by Eugene Delacroix, 1840

A great army is raised by a coalition of Western Christian nations to invade a Muslim land in the Mideast. But the army’s corrupt leaders change course and instead attack the capital city of a Christian land that is run by what they consider to be an evil and illegitimate dictator, a land that has strayed from the True Church, and that evidence suggests may secretly be in league with the Muslims.

A lot of Western troops desert and go home, because that’s not what they signed up for.

The Westerners attack the city, causing much destruction and burning down a large portion of it. The evil dictator flees, taking much of the city’s treasury with him. The Westerners expect to be welcomed as saviors, as liberators, but the local populace hates them. The citizens have another leader of their own and reject the leader provided by the invaders. The Westerners kill many local people, loot all the wealth of the churches and palaces, rape many local Christian women - and accidentally burn down another large portion of the city. The local citizens constantly attack the invaders in the streets, forcing them to withdraw into a well-fortified ghetto. The Westerners still don’t understand why they aren’t welcomed as liberators. The Westerners eventually impose their own government on the city, but many local leaders leave and set up competing governments in outlying areas, attacking the Westerners whenever they can. It is all downhill from there. The Westerners stay, but everything is a mess. And 57 years later, the local people finally win their city back and drive out the Westerners.

Any of that sound familiar?

It was the Fourth Crusade, which was redirected against Constantinople and which is now viewed as one of the great crimes of the Middle Ages.