Westphalia's religious settlement is the war's longest shadow. The peace admitted Calvinism to the legal standing that Lutheranism and Catholicism had held since 1555, fixed 1624 as the normal year by which the confession of each territory and the ownership of every church, monastery and endowment would be judged, and paired the ruler's right to set his territory's religion with new rights for dissenting subjects to worship privately and to emigrate. The confessional map of Germany froze roughly along the lines it holds today, a Protestant north and east against a Catholic south and west, and the Empire's courts, staffed in confessional parity, spent the next century adjudicating the details.
Whether the Thirty Years War was in fact a war of religion is one of the standing arguments of early modern history. Confession organised its alliances, its propaganda and its atrocities, from the sack of Magdeburg to the fate of Bohemian Protestantism, yet France's conduct, the Protestant princes who fought for the emperor, and the mercenary armies indifferent to creed all cut across the confessional lines, and Wilson's history argues that the crisis of the Empire's constitution, not faith itself, drove the war. The safest summary may be that religion made the war possible and politics made it endless.
Its cultural deposit is deep: the devastation shaped German hymnody and piety, Grimmelshausen's Simplicissimus turned it into the first great German novel, and the treaty's name became a byword, argued over by historians, for the modern order of sovereign states.