What year marks the start of the Protestant Reformation initiated by Martin Luther?

The Protestant Reformation began in 1517 when Martin Luther famously nailed his Ninety-Five Theses to the door of the Wittenberg Castle Church in Germany. This act is widely recognized as the catalyst for the widespread movement that challenged the practices and doctrines of the Catholic Church, leading to the establishment of various Protestant denominations. Luther's Theses addressed issues like the sale of indulgences and the authority of the pope, setting off a theological debate that transformed Christianity in Europe.

The significance of 1517 is not only about the act itself but also about how it symbolized a collective questioning of the religious status quo and the beginning of a major historical shift toward individual interpretation of the Bible and religious practices. This year marked the start of profound changes in ecclesiastical authority, contributing to the eventual rise of modern nation-states influenced by these new religious ideas.