The Thirty Years’ War was a 17th-century religious conflict fought primarily in central Europe. It remains one of the longest and most brutal wars in human history, with more than 8 million casualties resulting from military battles as well as from the famine and disease caused by the conflict. The war lasted from 1618 to 1648, starting as a battle among the Catholic and Protestant states that formed the Holy Roman Empire. However, as the Thirty Years’ War evolved, it became less about religion and more about which group would ultimately govern Europe. In the end, the conflict changed the geopolitical face of Europe and the role of religion and nation-states in society.