Short answers, pulled from the story.
The Peace of Westphalia ended the Thirty Years' War (1618-1648) and brought peace to the Holy Roman Empire. It also coincided with the formal end of the Eighty Years' War between the Dutch Republic and Spain, concluded by a separate treaty signed in Münster on the 30th of January 1648.
Talks were split between Münster and Osnabrück because each side wanted to meet on territory under its own control. Münster was a strictly Catholic city, acceptable to the Habsburg and French delegations, while Sweden insisted on negotiating in Protestant-leaning Osnabrück. Both cities were designated as neutral and demilitarized zones.
The Thirty Years' War alone killed between four and a half million and eight million people. The Peace of Westphalia's preamble referenced approximately eight million deaths across the broader period of European conflict that the treaties brought to a close.
The Peace of Westphalia gave Calvinism its first legal recognition as an official religion of the Holy Roman Empire, alongside Catholicism and Lutheranism. It also removed the right of rulers to force subjects to follow the ruler's own religion.
Sweden received an indemnity of five million thalers, Western Pomerania, Wismar, and the Prince-Bishoprics of Bremen and Verden as hereditary fiefs. These gains gave Sweden a seat and vote in the Imperial Diet of the Holy Roman Empire.
The Westphalian myth is the claim that the Peace of Westphalia established the modern principles of state sovereignty and non-interference in international law. Most modern historians reject this view because the treaties' text contains no such principles; the passages on sovereignty address only the internal constitutional arrangements of the Holy Roman Empire. Scholars trace the modern interpretation to nineteenth- and twentieth-century theorists rather than to the 1648 texts themselves.