One hundred and ninety-four European rulers, great and small, were represented at the Congress of Westphalia, and talks went on constantly from the spring of 1643 until the autumn of l648. The outstanding issues of the war were solved in two phases: the first, which lasted from November 1645 until June 1647, saw the chief imperial negotiator, Maximilian, Count Trauttmannsdorf, settle most issues; the second, which continued from then until the treaty of peace was signed in October 1648, saw France try to sabotage the agreements already made.

The purely German problems were resolved first, partly because they were already near solution and partly because the foreign diplomats realized that it was best (in the words of the count d’Avaux, the French envoy)

to place first on the table the items concerning public peace and the liberties of the Empire…because if the German rulers do not yet truly wish for peace, it would be…damaging to us if the talks broke down over our own particular demands.

So in 1645 and 1646, with the aid of French and Swedish mediation, the territorial rulers were granted a large degree of sovereignty (Landeshoheit), a general amnesty was issued to all German princes, an eighth electorate was created for the son of Frederick V (so that both he and Maximilian possessed the coveted dignity), the Edict of Restitution was finally abandoned, and Calvinism within the empire was granted official toleration. The last two points were the most bitterly argued and led to the division of the German rulers at the Congress into two blocs: the Corpus Catholicorum and the Corpus Evangelicorum. Neither was monolithic or wholly united, but eventually the Catholics split into those who were prepared to make religious concessions in order to have peace and those who were not. A coalition of Protestants and pragmatic Catholics then succeeded in securing the acceptance of a formula that recognized as Protestant all church lands in secular hands by January 1, 1624 (that is, before the gains made by Wallenstein and Tilly), and granted freedom of worship to religious minorities where these had existed by the same date. The Augsburg settlement of 1555 was thus entirely overthrown, and it was agreed that any change to the new formula must be achieved only through the “amicable composition” of the Catholic and Protestant blocs, not by a simple majority.

The amicable composition principle was finally accepted by all parties early in l648, thus solving the last German problem. That this did not lead to immediate peace was due to the difficulty of satisfying the foreign powers involved. Apart from France and Sweden, representatives from the Dutch Republic, Spain, and many other non-German participants in the war were present, each of them eager to secure the best settlement they could. The war in the Netherlands was the first to be ended: on January 30, 1648, Philip IV of Spain signed a peace that recognized the Dutch Republic as independent and agreed to liberalize trade between the Netherlands and the Iberian world. The French government, led since Richelieu’s death (December 4, 1642) by Jules Cardinal Mazarin (Giulio Mazzarino), was bitterly opposed to this settlement, since it left Spain free to deploy all its forces in the Low Countries against France; as a consequence, France devoted all its efforts to perpetuating the war in Germany. Although Mazarin had already signed a preliminary agreement with the emperor in September 1646, which conveyed parts of Alsace and Lorraine to France, in 1647–48 he started a new campaign in Germany in order to secure more. On May 17, l648, another Bavarian army was destroyed at Zusmarshausen, near Nördlingen, and Maximilian’s lands were occupied by the French.

Mazarin’s desire to keep on fighting was thwarted by two developments. On the one hand, the pressure of the war on French taxpayers created tensions that in June l648 erupted into the revolt known as the Fronde. On the other hand, Sweden made a separate peace with the emperor. The Stockholm government, still directed by Oxenstierna, was offered half of Pomerania, most of Mecklenburg, and the secularized bishoprics of Bremen and Verden; it was to receive a seat in the Imperial Diet; and the territories of the empire promised to pay five million thalers to the Swedish army for its wage arrears. With so many tangible gains, and with Germany so prostrated that there was no risk of any further imperial attack, it was clearly time to wriggle out of the war, even without France; peace was thus signed on August 6.

Without Sweden, Mazarin realized that France needed to make peace at the earliest opportunity. He informed his representatives at the Congress:

It is almost a miracle that…we can keep our affairs going, and even make them prosper; but prudence dictates that we should not place all our trust in this miracle continuing for long.

Mazarin therefore settled with the emperor on easy terms: France gained only the transfer of a bundle of rights and territories in Alsace and Lorraine and little else. Mazarin could, nevertheless, derive satisfaction from the fact that, when the ink dried on the final treaty of October 24, l648, the emperor was firmly excluded from the empire and was under oath to provide no further aid to Spain. Mazarin settled down to suppress the Fronde revolt and to win the war against Philip IV.