The causes of the Thirty Years War can be traced as far back as the renaissance period. It was during the renaissance that such ideals as secularism, humanism, individualism, rationalism and above all else secularism were first apparent in main stream society. These ideas led to the protestant reformation, which is an even more direct cause of the war.
The split of the Catholic Church, as a result of the protestant reformation left Europe in a state of religious turmoil and chaos. The gradual increase in intolerance and religious sectionalism that coincided with the addition of new religions and even more diversity has been marked as the main cause of the Thirty Years War. The effects of the war would prove to be devastating to most of Europe, evidenced by the sharp drop in population, but it was especially devastating to Germany. However, there were some countries and bodies of people that emerged from the conflict improved such as France, Sweden, and the religion of Calvinism. There were many territorial and dynastic issues that figured in the outbreak and conduct of the war as well, but it is believed that these factors did not become important until the middle stages of the war. The territorial and dynastic causes, which go hand in hand, did however, cause the war to continue longer than it most likely would have if religion had been the only motive.
The extent of religious motives therefor is debated, but cannot be dismissed. The immediate causes of the war began with the resistance and eventual revolt of Protestant nobles in Bohemia, due to the religious intolerance mentioned before, which was under Hapsburg domination, against the Catholic king Ferdinand. The reasons and causes for its spread throughout Europe include the constitutional frailty of the Holy Roman Empire, the inability of the German states to act in concert, and the ambitions of other European powers. These were the causes that would eventually be responsible for the war lasting as long as it did. The political motives became more and more prevalent when Sweden entered the war to help the Protestant cause. Sweden did not enter the war for religious reasons at all; they were looking to gain land.
Finally it seemed that religion was completely forgotten and abandoned as a cause when Catholic France and Protestant Sweden joined forces against the Catholic Hapsburgs. France was worried that the Hapsburgs were becoming too powerful so they decided to assert their influence into the war. The results and effects of the war and the two peace treaties were highly significant. France replaced Spain as the greatest power in Europe. With Sweden, France had blocked the Habsburg efforts to strengthen their authority in the Empire.
At Westphalia, the right of the individual states within the Empire to make war and conclude alliances was recognized. In theory as well as in fact, the most important of these states became virtually autonomous, and German unity was postponed for more than two centuries. The Empire was further dismembered by the recognition of the independence of Switzerland and the seven northern provinces of the Netherlands. Two new powers emerged in northern Germany.
France received most of Alsace by the Treaty of Westphalia, and by the Treaty of Pyrenees parts of Flanders and Artois in the Spanish Netherlands and lands in the Pyrenees. The religious settlement at Westphalia confirmed the predominance of Catholicism in southern Germany and of Protestantism in northern Germany. The principle accepted by the Peace of Augsburg of 1555 that Catholic and Lutheran princes could determine the religion practiced in their territory was maintained, and this privilege was extended to include the Calvinists as well. The Austrian Habsburgs had failed in their efforts to increase their authority in the Empire and to eradicate Protestantism, but they emerged from the war stronger than before. In Bohemia, they had stamped out Protestantism, broken the power of the old nobility, and declared the crown hereditary in the male line of their family.
With Bohemia now firmly in their grasp and with their large group of adjoining territories, they were ready to expand to the east in the Balkans, to the south in Italy, or to interfere once more in the