The event known for causing a major shift in the power structure of Europe during the 16th century was the Protestant Reformation. Initiated by figures like Martin Luther, who famously nailed his Ninety-Five Theses to a church door in 1517, the Reformation challenged the authority of the Catholic Church and altered the religious landscape of Europe. It questioned the practices and teachings of the Church, ultimately leading to the rise of Protestant denominations. This movement not only fostered significant religious conflict but also contributed to political changes, as rulers and states across Europe aligned with various religious factions, laying the groundwork for modern nation-states.