Pope Leo X is elected pope. He will forever be known as the pope of the beginning of Protestant Reformation because it's during his reign that Martin Luther reacts so negatively to many church excesses - and excesses for which Leo himself will be responsible.
Leo will engage is massive construction campaigns, expensive military campaigns, and huge personal extravagance, all of which force the Church into deep debt.
Pope Leo X will need to find a lot of new funds, so he will increase the sale of both ecclesiastical offices and of indulgences. This will protested throughout Europe as people grow increasingly weary of the corruption, scandals and excesses of the Church.