The event that marked the start of the Protestant Reformation was Martin Luther's posting of the Ninety-Five Theses in 1517. This document challenged the practices of the Catholic Church, particularly the sale of indulgences. Luther's actions sparked widespread debate and led to the emergence of various Protestant denominations. The Reformation not only challenged the authority of the Church but also encouraged a return to the scriptures and the idea of individual faith. As a result, it significantly reshaped the religious and political landscape of Europe, leading to conflicts such as the Thirty Years' War.