Ian Gould asks on Facebook: "What if the First Crusade (1096-99) ended in disaster at the Battle of Dorylaeum (where the Seljuks attacked one half of a divided Crusader army only to have the other half arrive during the battle) or at the siege of Antioch (the Crusaders took the city after an extended siege but then found themselves in turn besieged by Turkish reinforcements and were only saved the opportune arrival of another contingent of Crusaders).
"After the disaster of the earlier's People's Crusade might Europeans have simply given up on the idea of retaking Jerusalem?
"Would no fourth Crusade have meant the Byzantine Empire survived?
"Would the Reconquest of Spain and the conversion of the pagans of north eastern Europe have proceeded faster?
"Would the Age of Discovery have started sooner?"
Gavin Bowen writes: "The Fifth Crusade was a failed attempt by Christian crusaders to invade Egypt and reestablish Christian control in the Holy Land. After the Crusaders captured the port of Damietta the Egyptian Sultan offered the Crusaders control of the Holy land for return of the city. This offer was refused and the Crusaders were ultimately encircled and destroyed while attempting to march south and capture Cairo. What would have happened if they had succeeded in capturing Cairo and establishing a Christian state in Egypt? Could they have held onto it or would it have fallen like the Crusader States in the Levant?" Discussion on Facebook.