The most obvious reason for this conflict was religion - the culmination of the fervent struggle between Catholic and Protestant that had been ongoing since the Reformation. The long-established Holy Roman Empire which held sway over Central Europe and the German states, administered by the Catholic Habsburg dynasty, saw rebellion...
The most obvious reason for this conflict was religion - the culmination of the fervent struggle between Catholic and Protestant that had been ongoing since the Reformation. The long-established Holy Roman Empire which held sway over Central Europe and the German states, administered by the Catholic Habsburg dynasty, saw rebellion by Protestant princes in Bohemia in 1818. This rebellion was aided by another Protestant state, the German Palatinate led by Frederick V. Emperor Ferdinand II did succeed in suppressing this rebellion, but the precedent for revolt against the Imperial power of the Habsburgs had been set.
Other Protestant rulers were encouraged to challenge the Empire, notably King Christian IV of Denmark. He wanted to protect Protestant interests and also to increase Danish influence in Europe. He was beaten back by the emperor's brilliant general, Wallenstein, but then, in 1630 Gustavus Adolphus of Sweden took up the Protestant cause against the Empire. Although peace was made in 1635, the matter of the Imperial Habsburg influence was not allowed to rest. This time it was France who intervened, under Cardinal Richelieu. This was the clearest indication yet that this was not just a religious conflict, as France, like the Habsburg rulers was also Catholic; it was also a struggle for purely political ascendancy. Richelieu wanted to see Habsburg power in Europe curtailed. The French won significant victories against the emperor's armies before a general peace was finally established with the Treaty of Westphalia - a treaty which had important consequences for the future of Europe.
The Treaty of Westphalia allowed new rights and freedoms to the states under the Holy Roman Empire and in fact effectively broke up the empire leading to smaller fragmented states. This went some way, indeed, towards the concept of the modern sovereign state at the expense of vast, older-fashioned entities like the Holy Roman Empire. The Thirty Years' War also significantly shifted the balance of power in Europe. Habsburg-dominated Austria and also Spain, a former great European power, were left weakened, while France emerged as the strongest European nation with Sweden also gaining influence.
This war was the last major European mainland war to be fought in the name of religion - even although, as we have seen, there were significant secular interests at work as well. The war also saw great devastation wrought by the mercenary soldiers, particularly in the German states, and did much to lessen the role of mercenaries in warfare and to establish formal, orderly armies in Europe.