1198 Innocent III, wanting to restore Papal authority, preaches the Fourth Crusade. He did NOT write to kings at all - wanted nobles that he could have under his command. BUT they didn't have enough to pay them. At this point, Byzantium in turmoil. In 1203, after Crusader attacks on the city, Alexius IV takes over Constantinople.
Crusaders sit outside.
Alexius unable to deliver on his promises - and his people aren't too happy about the westerners. SO Crusades move from this initial outpouring of popular piety and adventure to something supposedly directed by the Pope, that no longer has Islam as its goal. The shape of the world itself had changed. For a wealth of related material, including a number of on-line texts, click here .