Due to small battles with the Muslims in Palestine, in the winter of 1218 King Andrew left - greatly weakening the crusader force. Although the King's leaving was a great loss, new reinforcements came in the spring and they devised a plan to take over Europe. However, King John of Jerusalem saw the advantages of taking over Egypt.
In 1218, the plan to take over Damietta, Egypt, a town in the Nile delta that protected the main route up river to Cairo, began.
Although Sultan Al-Adil of Damietta put up a fight, the crusaders managed to capture an important defensive tower on the river - a crucial step in the ensuing events to follow.
Sultan Al-Kamil, in a fit of desperation, offered the whole territory of Jerusalem.
King John and Cardinal Pelagius argued about whether to accept the offer, and in the end Pelagius won the disagreement when King John returned to Acre in 1220.
Pelagius received few reinforcements from Emperor Frederick II, a true military leader, who signed a vow of crusading in 1221. Due to all the miscommunication and disagreements between the crusaders, Al-Kamil was able to build up a great army at Mansourah.
Pelagius planned to take the Muslim camp quickly. However, when they saw what a magnificent military base Al-Kamil built, they were greatly surprised. Nevertheless, they crossed a dry river bed - not realizing it was flooding season. Before long the river swelled - effectively cutting off the crusaders from their supplies down river. Al-Kamil saw his chance and attacked the crusaders by flooding their camp. On 28th August 1221, the crusaders surrendered.