The main cause of the Thirty Years' War (1618–1648) was primarily religious conflict between Protestant and Catholic states within the Holy Roman Empire, alongside political power struggles. The war began with the Defenestration of Prague, where Protestant nobles rejected the authority of the Catholic Habsburgs. As the conflict escalated, it drew in various European powers seeking to gain influence or protect their religious affiliations, transforming into a broader political war. The war caused widespread devastation, particularly in Germany, and concluded with the Peace of Westphalia in 1648, leading to significant territorial and political changes in Europe.