The Thirty Years' War has been described as the last major European war of religion and the first all-European struggle for power. It was literally a series of wars, fought mainly on German soil, and was in large part a struggle to alter the European balance of power.
The common people bore the heavy cost of this devastating war. Historians disagree on precise figures; but in Northeastern Germany in Brandenburg, Mecklenburg, and Pomerania, and in Southwestern Germany in the Palatinate, Wurttemberg, and parts of Bavaria, population losses were believed to have been in excess of 50 percent.
The religious wars that had divided Germany and the Holy Roman Empire as a result of the Protestant Reformation ended with the Peace of Augsburg in 1555. The compromise produced a peace between the Protestant and Roman Catholic states of the empire that lasted for the next 50 years. However, in the early 17th century tensions between the rival faiths suddenly revived.
The Bohemian War marked the start of hostilities on May 23, 1618. At issue was the advance of royal power through the absolutist and Catholic policies of king Ferdinand of Habsburg, soon to be elected Holy Roman Emperor Ferdinand II. Both sides were convinced that they were fighting for a holy cause, with the fear of not only political defeat but annihilation if the other won. Both sides searched for allies, and as a result the conflict widened, entangling it with the religious and political struggles of their neighbors.
The Bohemians appealed to the Protestant Prince of Transylvania who was hoping to win the crown of Hungary from the Habsburgs. They also elected Frederick V of the Palatinate as their new king. They hoped that Frederick's father-in-law, James I of England, and his uncle, Maurice of Nassau, virtual ruler of the United Provinces of the Netherlands, would lend support.
Ferdinand called on his allies including Poland, his cousin Maximilian, Duke of Bavaria (leader of the Catholic League of German princes), and on the Habsburg king of Spain, Philip III. In 1620 the Bohemians were defeated at White Mountain near Prague, and Frederick V lost his crown as suddenly as he had won it. He continued to fight, employing various mercenary leaders, relying on English and Dutch assistance. In 1623, however, the Palatinate was overrun by Spanish and Bavarian troops, and Frederick's electoral vote was transferred to Maximilian of Bavaria.
The war had expanded in 1621 as the Dutch and Spanish renewed the struggle that had started two generations previously with the revolt of the Netherlands. Dutch and Spanish money and military expertise fueled much of the fighting in Europe. Spanish troops fought in Germany, Italy, and France. The Dutch, with a much smaller population, preferred to finance military allies. After Frederick's generals these allies included Christian IV of Denmark, who feared the continued victories of neighbor's armies. With Christian IV soon routed by Tilly, and victory apparently in hand, Emperor Ferdinand issued (Mar. 29, 1629) the Edict of Restitution, which restored to the Catholic church all property taken by the Protestants since 1552.
After Denmark's withdrawal from the war in May of 1629 another Scandinavian power joined the fray. Encouraged by France, Sweden concluded a truce with its Baltic rival Poland, and in July 1630 the Swedish king Gustav II Adolf landed in Pomerania to begin a series of victorious campaigns against the imperial armies. The Swedes were victorious in several battles in 1631 and 1632, although Gustav Adolf was killed in defeating Wallenstein in November of 1632.
Throughout these years, the Catholic King Louis XIII of France, the traditional rival of the house of Habsburg for preeminence in Europe, had observed Tilly's and Wallenstein's victories with increasing concern. He had waged several civil wars against his own Protestant subjects, the Huguenots. After defeating the Huguenots, France turned to fight Spain. After Gustav Adolf's death and after the Swedes suffered a severe defeat at Nordlingen on Sept. 6, 1634, France openly declared war in 1635 on Spain, Sweden, and some German Protestant princes.
The ring of alliances was virtually complete; no treaty between any two states, or even group of states, could now end the war. The intervention of France on the "Protestant" side cut across the religious alignments of the warring factions. Religious aims and motivation began to drop into the background. In 1640 Catholic Portugal rebelled against Catholic Spain. In 1643 the Protestant Christian of Denmark, fearing the increasing power of Protestant Sweden, restarted the old Danish-Swedish rivalry for the control of the Sound (Oresund), the northwestern entrance to the Baltic. Once more the Danes were heavily defeated and lost their monopoly control over the Sound.
Peace settlements began in 1643 with the ambassadors of the combatants meeting in peace congresses in Westphalia. The relative position of parties continued to change when there was no immediate truce, with all parties wanting to negotiate from a position of strength. Therefore it took 5 years to conclude peace, beginning in January 1648 between Spain and the United Provinces. October 1648 marked peace between France, Sweden, the Holy Roman emperor, and the German princes (Peace of Westphalia). The war between France and Spain continued until 1659 (Peace of the Pyrenees), despite Britain joining France against Spain in 1656. The wars between Sweden and Poland and between Sweden and Denmark flared up again and were not settled until 1660 (Peace of Oliva and Peace of Copenhagen).
The Peace of Westphalia solved some problems. The Habsburgs had failed
to reassert imperial power and the German princes were left with virtual
political independence and with the right to choose their religion. Their
subjects were given no such choice but were allowed to emigrate. In European
power politics, religion no longer determined alliances, nor did it lead
countries into war. Sweden had become the dominant power in the Baltic,
and France had displaced Spain as the dominant power in western Europe.