Explanation: The Crusades were a series of ultimately futile expeditions from Catholic Europe to the Levant in an attempt to conquer the 'Holy Land' from the Muslim polities which held it. They had some short-lived success in established outpost 'Crusader States', but within 300 years had lost everything, at immense cost in blood and treasure to the Catholic, Orthodox Christian, and Muslim polities involved.
... but two Catholic states made out like bandits, and not by plunder! Venice and Genoa were independent Italian city-states of the period with significant naval capacity - rather than engaging directly in warfare, they offered to ferry the Crusaders and their supplies to the Levant... but with a strict no non-payment policy. In God they trust - all others pay in silver!