Why did the Fourth Crusade didn't sail to Alexandria as originaly planned?

Answer 1

Cash troubles basically. The organisers had hoped for around 35,000 participants to depart from Venice, so they organised transport with the Venetians to Alexandria. The Venetians agreed to organise this, and reserved their whole fleet, merchant and war, for the crusaders that year. This was a huge financial risk since no normal trading would happen that year, so any profits would have to come from crusader payments and conquests (and the ensuing lucrative monopolies they were hoping for).

When the time had come to depart, only around 13,000 crusaders had arrived, so there was not enough cash to pay the Venetians the agreed sum of 85,000 ducats. That lead to the Venetians re-purposing the crusade for their own needs to make up for the loss. First they conquered Zara, and then they continued to Constantinople to effect a regime change.

The reason for the move to Constantinople were primarily to put a prince on the throne who had made promises to financially and militarily support the crusaders. Since the armies were still desperately short on cash, these promises seemed to solve all the crusader's problems in one go, so the decision was made to reroute to Byzantium.

Once there things escalated into violence quickly as the crusaders found out their prince had virtually no support and that force was needed to effect the regime change. This resulted in the infamous sack of Constantinople in 1204 after which the remaining crusaders set up the so called Latin Empire of Constantinople.

During the whole crusade many had already left because they didn't wanted to attack fellow Christians and/or face excommunication by the pope. Those who remained were now required to secure these new and very unstable states, so the end result was that almost none of the original crusaders went on to the Holy Land.

The only real winner as such would be Venice who knew the area very well and managed to gain a number of desirable trading ports and islands as well as exclusive trading consessions.