The Protestant Reformation was a seismic shift in Western Christianity that challenged the authority of the Catholic Church. Sparked by Martin Luther's 95 Theses in 1517, it spread across Europe, led by reformers like John Calvin and Huldrych Zwingli who advocated for salvation through faith alone and scripture as the ultimate authority. This movement reshaped religious, political, and social structures. It emphasized individual faith, vernacular Bible translations, and education. The Reformation's impact extended beyond religion, influencing the development of nation-states, religious pluralism, and even modern capitalism through the Protestant work ethic.