Thirty Years' War, a war or rather an uninterrupted succession of wars (1618–48) in Germany, in which Austria, most of the Catholic princes of Germany, and Spain were engaged on the one side throughout, but against different antagonists. This long-continued strife had its origin in the quarrels between the Catholics and Protestants of Germany, and few wars in modern times have caused more slaughter, misery, ruin, and demoralisation. The severe measures taken by the emperor, the head of the Catholic party, against the Protestants' religion led also to restrictions on their civil rights; and it was to protect their political as well as their religious liberties that the Protestants formed a union in 1608. The rival union of the Catholic powers followed in 1609. (1) Bohemian War (1618–20). The withdrawal of concessions to the Protestants of Bohemia by the Emperor Rudolf II. led to an insurrection in Prague and the election of Frederik V., the Elector Palatine, as king of Bohemia (1619); and Count Thurn repeatedly routed the imperial troops. But on 8th November 1620 a well-appointed army of 30,000, under Duke Maximilian of Bavaria, totally routed Frederick's motley array at Weissenberg near Prague, while an army of Spaniards under Spinola ravaged the Lower Palatinate. The Bohemians were now subjected to the most frightful tyranny and persecution.
(2) War of the Palatinate (1621–24). But the indomitable pertinacity and excellent leadership of Count Mansfield and Christian of Brunswick, two famous partisan leaders, who ravaged the territories of the Catholic league, did much to equalise the success of the antagonistic parties. Here the war might have ended; but the fearful tyranny of Ferdinand over all the Protestants in his dominions (Hungary excepted) drove them to despair, and the war advanced to its third phase.
(3) Danish-Saxon War (1624–30). Christian IV. of Denmark, smarting under some injuries inflicted on him by the emperor, and aided by a British subsidy, came to the aid of his German co-religionists in 1624, and, being joined by Mansfield and Christian of Brunswick, advanced into Lower Saxony. But when, by the aid of Wallenstein, a powerful army had been obtained, and the leaguers under Tilly, in co-operation with it, had marched northwards, the rout of the Danes by Tilly at Lutter, and of Mansfield by Wallenstein at Dessau, again prostrated the Protestants' hopes in the dust; yet a gleam of comfort was obtained from the victorious raid of Mansfield through Silesia, Moravia, and Hungary. The combined imperialists and leaguers meantime had overrun North Germany and continental Denmark, and ultimately compelled King Christian to conclude the humiliating peace of Lünebeck.
(4) Swedish-German War (1630–36). Ferdinand, not content with a still more rigorous treatment of the Protestants, and the promulgation of the Restitution Edict, which seriously offended even the Catholics, stirred up Poland against Sweden, and insulted Gustavus Adolphus; and the war entered its fourth stage on the landing of the Swedes at Usedom (June 1630), and their conquest of Pomerania and Mecklenburg. Gustavus induced the Elector of Brandenburg to aid him; and though unable to save Magdeburg, he marched to join the Saxons, completely routed Tilly at Breitenfeld (1631), victoriously traversed the Main and Rhine valleys, again routed Tilly on the Lech (1632), and entered Munich. By the judicious strategy of Wallenstein he was however compelled to retire on Saxony, where he gained the great victory of Lützen (1632); but his death there, depriving the Protestants of the only man who could force the confederate powers to preserve unity of action, was a severe blow to their cause; though the genius and indefatigable zeal of his chancellor, Oxenstierna, and the brilliant talents of the Swedish generals, preserved the advantages they had gained, till the crushing defeat of Bernard of Weimar at Nordlingen (1634) again restored to the emperor a preponderating influence in Germany. Saxony now made peace at Prague (1635).
(5) Swedish-French War (1636–48). Final success now appeared to demand only one more strenuous effort on the part of Austria; but Oxenstierna, resolved to preserve to Sweden her German acquisitions, propitiated Richelieu (q.v.) by resigning to him the direction of the war; and the conflict advanced into its final and most extended phase. The emperor, allied with the Lutherans, was now also assailed through his ally, Spain, who was attacked on her own frontier, in the Netherlands, and in Italy; Bernard of Weimar, fighting independently, opposed the leaguers; while the Swedes, under Baner, held North Germany, and by frequent flying marches into Silesia and Bohemia distracted their opponents, and prevented them, after their successes over Duke Bernard, from proceeding with the invasion of France. The great victory of Baner over the Austrians and Saxons at Wittstock (1636) restored to Sweden the victor's wrath; and from this time, especially under Torstensohn and Konigsmark, the Swedes were always successful, adding a second victory of Breitenfeld (1642) and one at Jankau (1645) to their already long list of successes, and carrying devastation and ruin even to the gates of Vienna. On the Rhine the leaguers at first had great success; but after the Spanish power had been thoroughly broken in the Netherlands by Condé the French were reinforced on the Rhine, and under Condé and Turenne rolled back the leaguers through the Palatine and Bavaria, and revenged at Nordlingen (3d August 1645) the former defeat of the Swedes. The emperor was now deserted by all his allies except the Duke of Bavaria, whose territories were already mostly in the hands of Turenne and Wrangel; and a combined invasion of Austria from the west and north was on the point of being executed when, after seven years of diplomatic shuffling, the Peace of Westphalia (q.v.) put an end to this terrible struggle.
See the articles on the principal leaders in the struggle, especially Gustavus Adolphus and Wallenstein, and works there cited; Professor A. W. Ward's Thirty Years' War (1869), S. R. Gardiner's Thirty Years' War (1874); and German works by Schiller (Eng. trans. 1846), Soltl, Barthold, Gindely (Eng. trans. 2 vols. 1885), &c.