There were several conflicts that comprised the Thirty Years' War, and they had many different, specific causes. This answer will therefore only deal with the more general causes. The fundamental cause of these conflicts was unresolved tension between Catholics and Protestants in Europe, especially within the dozens of German principalities. The peace of Augsburg had sought to alleviate these tensions, but failed for a number of reasons, including the rise of Calvinism. The other general cause of the Thirty Years' War was, again very generally speaking, a series of dynastic and territorial struggles, again involving contested areas within Germany. These squabbles pulled in, at various points, the Spanish Habsburgs, Swedish, French, and Danish monarchs, and a number of lesser rulers. Their aims varied, and were usually related to advancing dynastic claims.