These treaties ended the Thirty Years' War (1618–1648) in the Holy Roman Empire, with the Habsburgs and their Catholic allies on one side, and the Protestant powers (Sweden, Denmark, Dutch, and Holy Roman principalities) and France (Catholic but anti-Habsburg) on the other. The treaties also ended the Eighty Years' War (1568–1648) between Spain and the Dutch Republic, with Spain formally recognising the independence of the Dutch Republic. The Treaties of Westphalia brought to a close a tumultuous period of European history which saw the deaths of approximately eight million people.
The negotiation process was lengthy and complex. Talks took place in two different cities, as both sides wanted to meet on territory under their own control. A total of 109 delegations arrived to represent the belligerent states, but not all delegations were present at the same time. Three treaties were signed to end each of the overlapping wars: the Peace of Münster, the Treaty of Münster, and the Treaty of Osnabrück. Collectively, these treaties make up the Peace of Westphalia.
The Peace of Westphalia established the precedent of peaces established by diplomatic congress. A new system of political order arose in central Europe, which political scientists now call Westphalian sovereignty, based upon the concept of co-existing sovereign states. Inter-state aggression was to be held in check by a balance of power, and a norm was established against interference in another state's domestic affairs. As European influence spread across the globe, these Westphalian principles, especially the concept of sovereign states, became central to international law and to the prevailing world order.
Peace negotiations between France and the Habsburgs began in Cologne in 1641. These negotiations were initially blocked by France, as Cardinal Richelieu of France desired the inclusion of all of its allies, whether fully sovereign countries or states within the Holy Roman Empire. In Hamburg and Lübeck, Sweden and the Holy Roman Empire negotiated the Treaty of Hamburg with the intervention of Richelieu. The Holy Roman Empire and Sweden declared the preparations of Cologne and the Treaty of Hamburg to be preliminaries of an overall peace agreement.
In Münster, negotiations took place between the Holy Roman Empire and France, as well as between the Dutch Republic and Spain. Münster had been, since its re-Catholicisation in 1535, a strictly mono-denominational community. It housed the Chapter of the Prince-Bishopric of Münster. Only Roman Catholic worship was permitted, while Calvinism and Lutheranism were prohibited.
Sweden preferred to negotiate with the Holy Roman Empire in Osnabrück, which the Protestant forces controlled. Osnabrück was a bidenominational Lutheran and Catholic city, with two Lutheran churches and two Catholic churches. The city council was exclusively Lutheran, and the burghers were mostly Lutheran, but the city also housed the Catholic Chapter of the Prince-Bishopric of Osnabrück and had many other Catholic inhabitants. Osnabrück had been subjugated by troops of the Catholic League from 1628–33 and then taken by Lutheran Sweden.