Though many of the events were outside the traditional time-period of the Middle Ages, the end of the unity of the Western Church (the Protestant Reformation), was one of the distinguishing characteristics of the medieval period. The Catholic Church had long fought against heretic movements, but during the Late Middle Ages, it started to experience demands for reform from within. The first of these came from Oxford professor John Wycliffe in England. Wycliffe held that the Bible should be the only authority in religious questions, and he spoke out against transubstantiation, celibacy and indulgences. In spite of influential supporters among the English aristocracy, such as John of Gaunt, the movement was not allowed to survive. Though Wycliffe himself was left unmolested, his supporters, the Lollards, were eventually suppressed in England.
What was the event that ended religious unity in the Western Church? (If the question is unanswerable, say "unanswerable")
the Protestant Reformation