No true Diet or Reichstag had been assembled since 1613. The Emperors, Ferdinand II and III both, had ruled by fiat and the consent of the Electors.
While they had hoped to resolve matters themselves, the Electors themselves, at the Kurfürstentag opened in Nürnberg on 3 February 1640, agreed that a Diet should be called. It was to debate a broader amnesty than that granted by the Peace of Prague in the hopes of at last bringing peace to the Empire.
The Diet actually opened at Regensburg on 13 September 1640. At first all went according to the Imperial plan. A safe-conduct was issued to emissaries from Hesse-Cassel and Brunswick-Lüneberg and even to the Winter King’s relict, Elizabeth Stuart. The Diet agreed to a general amnesty. And to put some force behind these pacific plans, the current size of, and subsidies to, the Imperial army were agreed.
In 1640 a short pamphlet, styled Dissertatio de ratione Status in Imperio nostro Romano-Germanico was published under the pseudonym Hippolithus à Lapide. This work, widely attributed to the Swedish court historiographer Bogislav von Chemnitz, demonstrated the actual weakness of the Emperors under the Imperial constitution and the manner in which the Habsburgs had exceeded their rightful authority in pursuit of power.
Widely read, this work cast under suspicion every action taken by Ferdinand III.
In December, 1640, Georg-Wilhelm, Elector of Brandenburg, died. He was succeeded by his son, Frederich-Wilhelm, soon to be known as the Great Elector.
In January, 1641, Frederich-Wilhelm removed his father’s advisor, the pro-Imperial Schwartzenberg. In July, 1641 he concluded a two-years’ truce with Sweden.
He then announced to the shocked Diet that he did not consider the Imperial proposals, grounded on an extension of the Peace of Prague and seeking a purely domestic solution to the wars of the Empire, worthy of his support.
The lesser Protestant princes immediately began to distance themselves from the Emperor and rally to the Brandenburger.
In December, 1640 the armies of Sweden, France and Brunswick again re-assembled at Erfurt for a combined campaign. As with the prior years campaign, the combined offensive accomplished nothing. Banér spent all his energies quarrelling with the French commander de Guebriant.
The allied forces penetrated as far south as the Danube at Regensburg, where the Diet was still sitting. In January, 1641, they briefly invested the city, but the Danube thawed and the half-hearted siege was lifted. The allied forces split up and retired to their bases.
Upon his return from the central German campaign, Banér sickened and, on 20 May, 1641, died. His army, whose discipline had always been suspect, began to rise in mutiny.
Shortly after the death of Banér, Sweden’s some-time ally Georg of Brunswick-Lüneberg also died.
Oxenstierna appointed Lennart Torstensson, general of artillery under Gustavus, as commander of the Swedish forces. In the interim, the armies were to be under the control of Wrangel. Although the Swedes were successful in driving off an Imperial force under Piccolomini sent to relieve the besieged Imperial stronghold of Wolfenbüttel, the Swedes were unable to follow up on their success.
Torstensson arrived in November, 1641. With him came 7,000 fresh Swedish recruits. Torstensson was able to restore discipline by brutally punishing the rebellious soldiery and leavening Banér’s old units with new, more loyal, Swedish conscripts.
During the summer of 1641, the Swedes and French had shown that, regardless of the Emperor’s wishes, they were not going to disappear from the Empire, nor were they going to permit any solution to be reached of which they were not a part.
On 30 June 1641, they entered into the Treaty of Hamburg, which renewed their 1638 treaty of alliance, which was set to expire. Unlike prior treaties, which had run for a specified term, this was to last until the war was over.
Secondly, the Swedes and French issued an invitation to the Emperor, Spain and the Estates of the Empire to peace conferences to be held in Westphalia.
The talks were to be segregated by religion. The Emperor, the Swedes and the Protestant princes, as well as the Spanish and the Dutch, were to negotiate at Osnabrück. The Emperor, the French, the Catholic Princes and the Spaniards were to negotiate at nearby Münster.
In December, 1641, both the Austrian and Spanish branches of the House of Austria accepted the invitation. The talks were scheduled to open in May, 1642.
In October, 1641 the Diet of Regensburg at last concluded. Little had been accomplished.
The Diet issued legislation promising Imperial amnesty to anyone who would lay down arms, renounce foreign alliances and reconcile with the Emperor.
Further, Ferdinand III arranged for a Deputationstag, a meeting of the Electors and other Princes to convene at Frankfort-am-Main. The representatives were to work out a plan for peace in the Empire. The Swedes and French were pointedly not invited. The Emperor’s goal was to resolve all internal problems at Frankfort and then negotiate with the foreigners with the entire Empire at his back.
The Welf dukes of Brunswick had fought adeptly on both sides of the war under the leadership of Georg of Brunswick-Lüneberg. He had fought first alongside Wallenstein, had been among the first of Gustavus’s German allies, had adhered to the Peace of Prague, and had allied himself with Sweden and France once again thereafter.
After Georg died, however, the remainder of his family lacked the cunning to follow in his footsteps. Their territories had been ravaged in 1641, first by invading Imperials and then by relieving Swedish allies.
The Brunswick dukes were willing to make peace, even at the price of giving over the Bishopric of Hildesheim to Catholicism. In January, 1642 the Emperor and the Brunswick dukes signed the Peace of Goslar; Brunswick was to be neutral for the remainder of the war.
Having quelled the disorders in Banérs former army, Torstensson went on the offensive in the spring of 1642. Striking east he defeated the Elector of Saxony’s forces at Schweidnitz.
With the road into the Imperial lands thus opened, the moved southeast into Moravia, taking the capital Omoluoc (Olmütz) in June, 1642. Torstensson fortified the place which was to serve as the linchpin of Swedish-held territory in the east for the remainder of the war.
With Vienna threatened, the Emperor assembled a large force under Piccolomini and Archduke Leopold. Torstensson fell back through Silesia and besieged Leipzig in Saxony.
On 2 November, 1642, the Imperial forces caught up with the Swedes. Torstensson, outnumbered, fell back on Breitenfeld. While the Imperials were yet assembling into their ranks, Torstensson led his army against the enemy left. They charged through a deadly cannonade, broke the Imperials and rolled up the remainder of the Habsburg army.
In this second battle of Breitenfeld, the Imperials lost half their army dead or prisoner. Leipzig fell within the month.
On 4 December, 1642, Armand-Jean du Plessis—Cardinal Richelieu—died. His health had long been weak and he had persisted in his labors only by dint of his preternatural will. He was succeeded as Louis XIII’s chief minister by the Sicilian Giulio Mazarini, more commonly known as Cardinal Mazarin.