Also, the Fourth Crusade pretty much doomed the Byzantine Empire, which never really recovered. Constantinople, a shadow of its former self, was conquered by the Turks in 1453. So ultimately, the crusades were a total failure at establishing Christian kingdoms in the Holy Land long term. And with the coming of the Ottomans, the region remained solidly Muslim, as it mostly is today. And the crusades didn't really open up lines of communication between the Christian and Muslim worlds, because those lines of communication were already open. Plus, most historians now agree that the crusades didn't bring Europe out of the Middle Ages by offering it contact with the superior intellectual accomplishments of the Islamic world. In fact, they were a tremendous drain on Europe's resources.