The Crusades - Pilgrimage or Holy War?: In which John Green teaches you about the Crusades embarked upon by European Christians in the 12th and 13th centuries. Our traditional perception of the Crusades as European Colonization thinly veiled in religion isn't quite right. John covers the First through the Fourth Crusades, telling you which were successful, which were well-intentioned yet ultimately destructive, and which were just plain crazy. Before you ask, no, he doesn't cover the Children's Crusade, in which children were provoked to gather for a Crusade, and then promptly sold into slavery by the organizers of said Crusade. While this story is charming, it turns out to be complete and utter hooey.