The Reformation significantly changed the political landscape in Germany, France and England and culminated in the Thirty Years' War of the 17th century. The most important political consequence of the Protestant Reformation was the Thirty Years' War between Catholics and Protestants, from 1618 to 1648. Involving nearly every major European country, the war was the worst Europe had ever seen, with over 8 millions of deaths. The war saw the decline of Catholic influence and Habsburg supremacy, as well as the establishment of the concept of nation-states through the Peace of Westphalia, a treaty that introduced the concept of a balance of power between the nations of Europe in the hope of prevent future conflicts. Germany at the time of the Reformation was not one country but a collection of unified principalities under the Holy Roman Emperor, who retained limited authority. Immediately after Luther's call for reform, many German princes converted to Protestantism and in 1531 formed the Schmalkaldic League in opposition to the Catholic-Habsburg Holy Roman Emperor, Charles V. After a long