The Christian Church initially started the practice of granting indulgences to Crusaders who took up the cross to free the Holy Land during the First Crusade. These indulgences were meant to wipe away the sins of those who received them. Over the next several hundred years the practice of granting indulgences eventually spread to the point where anyone could buy them for themselves and loved ones. Indulgences created a lot of money for the church and its many building projects. The practice of selling indulgences is also one of the main reasons that Martin Luther broke away from the Catholic Church in Rome. So the question is: If Pope Urban II had not created indulgences to recruit Crusaders in 1095 would the Protestant religions ever have formed?

(The Great Courses – How the Crusades Changed History)