The historical cause of the Protestant Reformation was primarily the discontent with the practices and beliefs of the Roman Catholic Church in the 16th century. Key issues included the sale of indulgences, corruption, and the Church's authority. Martin Luther's 95 Theses in 1517 highlighted these grievances, calling for reform and challenging papal authority. The desire for a more personal and direct relationship with God, along with the emergence of humanist ideas, further fueled the movement. The Reformation led to the establishment of various Protestant denominations and significantly altered the religious, political, and cultural landscape of Europe.