The Peace of Westphalia 1648 The Peace of Westphalia negotiated at Osnabrück and Münster, which ended the Thirty Years War (1618-48), is the key peace agreement of the early modern period; it also secured the domestic peace of the Holy Roman Empire until 1806. The peace congress which met from 1643 to 1649 was furthermore the first pan-European peace conference and it set a pattern for subsequent European peace congresses. It was a congress of ambassadors who developed a novel mode of negotiation; they acted upon and contributed to the developing notion of international law; and they developed distinctive solutions which set important precedents. This chapter begins with a survey of the background of the Thirty Years War. It then examines the content of the peace treaties and the significance of the Peace of Westphalia as a point of reference for future peace negotiations.