The emperor and his German allies, nevertheless, did remain united over the Edict of Restitution: there were to be no concessions in matters of religion and no restoration of forfeited lands. As a result, the German Protestants were driven reluctantly into the arms of Sweden, whose army was increased with the aid of subsidies secured from France and the Dutch. In September 1631 Gustav at last felt strong enough to challenge the emperor’s forces in battle: at Breitenfeld, just outside Leipzig in Saxony, he was totally victorious. The main Catholic field army was destroyed, and the Swedish Protestant host overran most of central Germany and Bohemia in the winter of 1631–32. The next summer they occupied Bavaria. Although Gustav died in battle at Lützen on Nov. 16, 1632, his forces were again victorious and his cause was directed with equal skill by his chief adviser, Axel Oxenstierna. In the east, Sweden managed to engineer a Russian invasion of Poland in the autumn of 1632 that tied down the forces of both powers for almost two years. Meanwhile, in Germany, Oxenstierna crafted a military alliance that transferred much of the cost of the war onto the shoulders of the German Protestant states (the Heilbronn League, April 23, 1633). Swedish ascendancy, however, was destroyed in 1634 when Russia made peace with Poland (at Polyanov, June 4) and Spain sent a large army across the Alps from Lombardy to join the imperial forces at the Battle of Nördlingen (September 6). This time the Swedes were decisively beaten and were obliged to withdraw their forces in haste from most of southern Germany.
Yet Sweden, under Oxenstierna’s skillful direction, fought on. Certainly its motives included a desire to defend the Protestant cause in Germany and to restore deposed princes to their thrones; but more important by far was the fear that, if the German Protestants were finally defeated, the imperialists would turn the Baltic into a Habsburg lake and might perhaps invade Sweden. The Stockholm government therefore desired a settlement that would atomize the empire into a jumble of independent, weak states incapable of threatening the security of Sweden or its hold on the Baltic. Furthermore, to guarantee this fragmentation, Oxenstierna desired the transfer to his country of sovereignty over certain strategic areas of the empire—particularly the duchy of Pomerania on the Baltic coast and the electorate of Mainz on the Rhine.
These, however, were not at all the goals of Sweden’s German allies. They aimed rather at the restoration of the prewar situation—in which there had been no place for Sweden—and it soon became clear that they were prepared to make a separate settlement with the emperor in order to achieve it. No sooner was Gustav dead than the elector of Saxony, as “foremost Lutheran prince of the Empire,” put out peace feelers toward Vienna. At first John George (1611–56) was adamant about the need to abolish the Edict of Restitution and to secure a full amnesty for all as preconditions for a settlement; but the imperial victory at Nördlingen made him less demanding. The insistence on an amnesty for Frederick V was dropped, and it was accepted that the edict would be applied in all areas recovered by Catholic forces before November 1627 (roughly speaking, this affected all lands south of the Elbe, but not the Lutheran heartland of Saxony and Brandenburg). The elector might have been required to make even more concessions but for the fact that, over the winter of 1634–35, French troops began to mass along the borders of Germany. As the papal nuncio in Vienna observed: “If the French intervene in Germany, the emperor will be forced to conclude peace with Saxony on whatever terms he can.” So the Peace of Prague was signed between the emperor and the Saxons on May 30, 1635, and within a year most other German Lutherans also changed their allegiance from Stockholm to Vienna. The European war in Germany, 1635–45
This partial settlement of the issues behind the war led many in Germany to look forward to a general peace. Certainly the exhaustion of many areas of the empire was a powerful incentive to end the war. The population of Lutheran Württemberg, for example, which was occupied by the imperialists between 1634 and 1638, fell from 450,000 to 100,000; material damage was estimated at 34 million thalers. Mecklenburg and Pomerania, occupied by the Swedes, had suffered in proportion. Even a city like Dresden, the capital of Saxony, which was neither besieged nor occupied, saw its demographic balance change from 121 baptisms for every 100 burials in the 1620s to 39 baptisms for every 100 burials in the 1630s. Amid such catastrophes an overwhelming sense of war-weariness engulfed Germany. The English physician William Harvey (discoverer of the circulation of blood), while visiting Germany in 1636, wrote:
The necessity they have here is of making peace on any condition, where there is no more means of making war and scarce of subsistence.…This warfare in Germany…threatens, in the end, anarchy and confusion.
Attempts were made to convert the Peace of Prague into a general settlement. At a meeting of the electors held at Regensburg in 1636–37, Ferdinand II agreed to pardon any prince who submitted to him and promised to begin talks with the foreign powers to discover their terms for peace. But the emperor’s death immediately after the meeting ended this initiative. Efforts by Pope Urban VIII (1623–44) to convene a general conference at Cologne were similarly unavailing. Then, in 1640, the new emperor, Ferdinand III (1637–57), assembled the Imperial Diet for the first time since 1613 in order to solve at least the outstanding German problems of the amnesty question and the restitution of church lands. He met with little success and could not prevent first Brandenburg (1641) and then Brunswick (1642) from making a separate agreement with Sweden. The problem was that none of these attempts at peace were acceptable to France and Sweden, yet no lasting settlement could be made without them.
After the Peace of Prague, the nature of the Thirty Years’ War was transformed. Instead of being principally a struggle between the emperor and his own subjects, with some foreign aid, it became a war of the emperor against foreign powers whose German supporters were, at most times, few in number and limited in resources. Sweden, as noted above, had distinct and fairly consistent war aims: to secure some bases in the empire, both as guarantees of influence in the postwar era and as some recompense for coming to the rescue of the Protestants, and to create a system of checks and balances in Germany, which would mean that no single power would ever again become dominant. If those aims could be achieved, Oxenstierna was prepared to quit. As he wrote:
We must let this German business be left to the Germans, who will be the only people to get any good out of it (if there is any), and therefore not spend any more men or money, but rather try by all means to wriggle out of it.
But how could these objectives be best achieved? The Heilbronn League did not long survive the Battle of Nördlingen and the Peace of Prague, and so it became necessary to find an alternative source of support. The only one available was France. Louis XIII and Richelieu, fresh from their triumph in Italy, had been subsidizing Sweden’s war effort for some time. In 1635, in the wake of Nördlingen, they signed an offensive and defensive alliance with the Dutch Republic (February 8), with Sweden (April 28), and with Savoy (July 11); they sent an army into the Alps to occupy the Valtelline, a strategic military link between the possessions of the Spanish and Austrian Habsburgs (March); and they mediated a 20-year truce between Sweden and Poland (September 12). Finally, on May 19, 1635, they declared war on Spain.
The aims of France were very different from those of Sweden and its German allies. France wished to defeat Spain, its rival for more than a century, and its early campaigns in Germany were intended more to prevent Ferdinand from sending aid to his Spanish cousins than to impose a Bourbon solution on Germany—indeed, France only declared war on Ferdinand in March 1636. Sweden at first therefore avoided a firm commitment to France, leaving the way clear for a separate peace should the military situation improve sufficiently to permit the achievement of its own particular aims. The war, however, did not go in favour of the allies. French and Swedish forces, operating separately, totally failed to reverse the verdict of Nördlingen: despite the Swedish victory at Wittstock (Oct. 4, 1636) and French gains in Alsace and the middle Rhine (1638), the Habsburgs always seemed able to even up the score. Thus, in 1641 Oxenstierna abandoned his attempt to maintain independence and threw in his lot with France. By the terms of the Treaty of Hamburg (March 15, 1641), the two sides promised not to make a separate peace. Instead, joint negotiations with the emperor and the German princes for the satisfaction of the allies’ claims were to begin in the Westphalian towns of Münster and Osnabrück. And, while the talks proceeded, the war was to continue.