 It was at the Peace of Westphalia in 1648 that Europe consolidated its long transition from the Middle Ages to a world of sovereign states. According to historian J.R. Strayer, Britain and France looked a lot like sovereign states by around 1300, their kings possessing supremacy within bounded territories. But as late as the beginning of the Reformation in 1517, Europe remained distant from Westphalia. It was just around then that a great reversal in historical momentum occurred when Charles V of Spain ascended to the throne, uniting Castile, Aragon and the Netherlands, at the same time becoming Holy Roman Emperor, gaining prerogatives over lands in Central Europe, while taking on the role of enforcer of the Catholic Church’s still significant temporal prerogatives inside the Empire, especially its enforcement of ecclesiastical orthodoxy. But within the Empire, Charles V was not sovereign, either, for princes and nobles there retained prerogatives over which he exercised no control. In 1555, a system of sovereign states gained important ground in the Peace of Augsburg, whose formula cuius regio, eius religio, allowed German princes to enforce their own faith within their territory. But Augsburg was unstable. Manifold contests over the settlement’s provisions resulted in constant wars, culminating finally in the Thirty Years War, which did not end until 1648, at the Peace of Westphalia.