To understand the Early Modern Era, one must recognize that religion was a profoundly powerful force in Europe (powerful in ways that it is difficult to fully appreciate from a modern, more secular perspective). People believed strongly in the supernatural, and when the Protestant Reformation shattered religious unity in Western...
To understand the Early Modern Era, one must recognize that religion was a profoundly powerful force in Europe (powerful in ways that it is difficult to fully appreciate from a modern, more secular perspective). People believed strongly in the supernatural, and when the Protestant Reformation shattered religious unity in Western Europe, it created a great deal of instability. The sixteenth and early seventeenth centuries constituted a very violent and tumultuous period with religious warfare, the witch craze, and sectarian violence. The Thirty Years War can be seen as the climax of this era in history. It was the last and most destructive of the Religious Wars, after which warfare and politics became more purely secular in nature.
The Thirty Years War began in the Holy Roman Empire, which was little more than a very loose collection made up of a vast number of political states and free cities. Unlike in other, more centralized polities of the Early Modern Era, where rulers were able to use royal authority to advance the interests of their own state religion, in the Holy Roman Empire religion was tied to the interests of the various princes, some of whom advanced Protestantism and others who advanced Catholicism within their own domains. In addition, there were the Hapsburg Emperors themselves.
So far, this explanation has largely been focused on the role of religion, but politics should not be overlooked either. Political centralization and religious uniformity often went hand in hand. Using royal authority to support or impose a state religion simultaneously served to advance the power and authority of the crown itself. This was also the case with the Emperor Ferdinand II: by advancing Catholic interests, he was also advancing his own political interests over competing power structures.
Ferdinand II had only recently inherited the Bohemia before succeeding to the position of Emperor. In seeking to impose Catholic supremacy through the suppression of Bohemian Protestants, he instigated a political crisis, where Bohemian Protestants ultimately rose in rebellion against the Emperor, offering rulership of Bohemia to the Protestant Frederick. From here the conflict would escalate, sparking a war that would devastate much of Central Europe.