[Sidenote: The Thirty Years' War: Ecclesiastical Causes] The peace of Augsburg (1555) had been expected to settle the religious question in the Germanies. But in practice it had failed to fix two important matters. In the first place, the provision forbidding further secularization of church property ("Ecclesiastical Reservation") was not carried out, nor could it be while human nature and human temptation remained. Every Catholic ecclesiastic who became Protestant would naturally endeavor to take his church lands with him. Then, in the second place, the peace had recognized only Catholics and Lutherans: meanwhile the Calvinists had increased their numbers, especially in southern and central Germany and in Bohemia, and demanded equal rights. In order to extort concessions from the emperor, a union of Protestant princes was formed, containing among its members the zealous young Calvinist prince of the Palatinate, Frederick, commonly called the Elector Palatine of the Rhine. The Catholics were in an equally belligerent frame of mind. Not only were they determined to prevent further secularization of church property, but, emboldened by the progress of the Catholic Reformation in the Germanies during the second half of the sixteenth century, they were now anxious to revise the earlier religious settlement in their own interest and to regain, if possible, the lands that had been lost by the Church to the Protestants. The Catholics relied for political and military support upon the Catholic Habsburg emperor and upon Maximilian, duke of Bavaria and head of the Catholic League of Princes. Religiously, the enemies of the Habsburgs were the German Protestants. [Sidenote: The Thirty Years' War: Political Causes] But a hardly less important cause of the Thirty Years' War lay in the politics of the Holy Roman Empire. The German princes had greatly increased their territories and their wealth during the Protestant Revolution. They aspired, each and all, to complete sovereignty. They would rid themselves of the outworn bonds of a medieval empire and assume their proper place among the independent and autocratic rulers of Europe. On his side, the emperor was insistent upon strengthening his position and securing a united powerful Germany under his personal control. Politically, the enemies of the Habsburgs were the German princes. With the princes was almost invariably allied any European monarch who had anything to gain from dividing Germany or weakening Habsburg influence. In case of a civil war, the Habsburgs might reasonably expect to find enemies in Denmark, Sweden, and France. [Sidenote: Four Periods in the Thirty Years' War] The war naturally divides itself into four periods: (1) The Bohemian Revolt; (2) The Danish Period; (3) The Swedish Period; (4) The French or International Period. [Sidenote: 1. The Bohemian Revolt]