The Avignon Papacy happened because Pope Boniface VIII issued the Unam Sanctam that declared that the power of the Pope was above all including the king. This did not please the kingdoms of France and England, especially during a time that the King of France wanted the Catholic Church to pay taxes. Pope Boniface VIII died under estrange circumstances and the new pope decided to not fo back to Rome and stay in Avignon, this period is also called the Catholic Schism.
This caused a series of problems for the Church because the College of Cardinals did not agree with the move to France and elected a Roman Pope, Urban VI. The Catholic Church had 2 popes and with a split rule countries started to take sides with each pope and the Church became a matter of politics.
All of these problems avoided the Catholic Church from making a series of reforms that were needed which made the numbers of critics and the abuses inside the Church rise. All of this eventually led to the Protestant Reform.
