The major cause of the Thirty Years' War was primarily the conflict between Protestant and Catholic states within the Holy Roman Empire, along with political power struggles involving neighboring European countries. The war began in 1618, rooted in rising tensions over religious freedoms and the governance of various principalities. The Defenestration of Prague, where Protestant nobles threw Catholic officials from a window, ignited the war. However, it escalated into a broader conflict involving France, Spain, and Sweden, among others, leading to devastating consequences in Europe and resulting in the Peace of Westphalia in 1648, which established territorial and religious resolutions.