After the first crusade, which successfully took back the Holy Land from the Muslims, and the unsuccessful second and third crusades, there was the disaster of the fourth crusade, which only further strained the relationship between the east and the west after the Great Schism.
The men who fought in the fourth crusade needed ships to sail from Venice to the Holy Land, so they made a deal with the Venetians. The doge (chief of an Italian state) of Venice offered a huge fleet, and unfortunately the messengers sent by the crusaders overestimated the amount of ships they needed and ended up agreeing to pay an amount which they could not afford. The doge was under great pressure to receive the money that was owed. This was because he called on the merchants to help prepare the fleet, which cost them greatly because they had not received anything for a year and a half. When he went to collect the money from the crusaders, they told him they weren’t able to pay the entire amount. They came to an agreement that they would pay the rest from their conquests gathered while on crusade.
The crusaders were told about a young man who was a claimant to the throne of Constantinople named Alexis. His brother, Alexis III, had taken the throne by treason, so it was deemed acceptable to try to assist him in taking the throne, in return for money to pay the Venetians. The crusaders then attacked the city of Constantinople and Alexis III fled. Alexis IV was crowned but did not pay all that he owed. He refused to pay more, so the Crusaders resolved to sack Constantinople.
The sacking of Constantinople was savage and ruthless. The crusaders’ behavior was appalling, destroying relics and sacred places. A Westerner named Baldwin of Flanders was put on the throne, and ruled for half a century. The Venetians were paid, but the main purpose of the crusade, to take back the Holy Land, was forgotten, except for a few loot-seeking knights and soldiers. The fourth crusade was a disaster, accomplishing nothing but the decimation of Constantinople and the complete loss of its standing in the world, not to mention furthering the divide between the East and the West.