A series of conflicts, fought mainly in Germany, in which Protestant–Catholic rivalries and German constitutional issues were gradually subsumed in a European struggle. It began in 1618 with the Protestant Bohemian revolt against the future emperor Ferdinand II; it embraced the last phase of the Dutch Revolts after 1621; and was concentrated in a Franco‐Habsburg confrontation in the years after 1635.

By 1623 Ferdinand had emerged victorious in the Bohemian revolt, and with Spanish and Bavarian help had conquered the Palatinate of Frederick V. But his German ambitions and his Spanish alliance aroused the apprehensions of Europe’s Protestant nations and also of France. In 1625 Christian IV of Denmark renewed the war against the Catholic imperialists, as the leader of an anti‐Habsburg coalition organized by the Dutch. After suffering a series of defeats at the hands of Tilly and Wallenstein, Denmark withdrew from the struggle at the Treaty of Lübeck (1629), and the emperor reached the summit of his power.

Sweden’s entry into the war under Gustavus II (Adolphus) led to imperial reversals. After Gustavus was killed at Lützen (1632), the Swedish Chancellor Oxenstierna financed the Heilbronn League of German Protestants (1633), which broke up after a heavy military defeat at Nördlingen in 1634. In 1635 the Treaty of Prague ended the civil war within Germany, but in the same year France, in alliance with Sweden and the United Provinces, went to war with the Habsburgs. Most of the issues were settled after five years of negotiation at the Treaty of Westphalia in 1648, but the Franco‐Spanish war continued until the Treaty of the Pyrenees in 1659.