The main contention in the Thirty Years' War was primarily driven by the conflict between Protestant and Catholic states within the Holy Roman Empire. It began in 1618 and evolved into a broader struggle involving various European powers. Central issues included religious freedom, political sovereignty, and the balance of power in Europe. Protestant states aimed to resist Catholic Habsburg dominance, while Catholic states sought to reclaim authority. The war had devastating effects, leading to massive loss of life, economic decline, and significant territorial and political changes through the Peace of Westphalia in 1648, which established the principle of state sovereignty and religious tolerance.