The Crusades had been called at the behest of the Byzantine (Orthodox) emperor, with the Catholics responding with no promise of reconciliation.
An ecumenical council of bishops from throughout the orthodox world, had met with Catholic bishops and determined there was no doctrinal basis for the schism, agreeing to reunite Rome and the East. But unlike the theologians, the kings of the East didn't like the political ramifications of the reconciliation, and scuttled it. In 1182, the citizens of Constantinople went on a rampage, and slaughtered 60,000 Latins, men, women and children who lived in Constantinople.
A Catholic-leaning emperor, Isaac II, ascended to the throne, eventually, however. He promised considerable support to the 4th crusade, but was dethroned. Against a papal threat of ex-communication, the Crusaders attacked Constantinople, seeking to re-establish Isaac II. Finding the city wealthy beyond their means (in contrast to their own kingdoms which were going bankrupt because of the Crusades), the Crusaders plundered the city.
Two and a half century later, including after two decades of assault by GREEK and ORTHODOX warlords, the Ottomans attacked. The Catholic pope tried to organize a Crusade among Orthodox and Catholic armies to defend Byzantium, but the Orthodox refused to help the Latins, or Constantinople. Abandoned by the rest of the Eastern Orthodox, Constantinople fell in 1452.
And to this day, the Greek Orthodox blame the Latins for the fall of Constantinople. Talk about dodging responsibility!
I hope some of the people who commented up above take the time to go back and read through the article, as it is clear they have some of the misconceptions that are cleared up in the article.