Evangelical ideas first reached Scandinavia around 1520. At this time, this vast and sparsely populated region was of only marginal political and religious significance in Europe. The Reformation of the Nordic countries which followed was largely a by-product of Luther's Reformation. The Nordic countries still remained of little importance for the Reformation in general, when, in 1555, the Peace of Augsburg guaranteed the survival of European Protestantism for the immediate future. However, by the early seventeenth century and the Thirty Years War, it was the political and military intervention of Lutheran Scandinavia, together with militant Calvinism in south and southwest Germany, which eventually secured the survival of Protestantism at the peace negotiations in Münster and Osnabrück. The importance of Scandinavia to European Protestantism less than a century after Luther's death was, in other words, paramount. Even if the interventions of Christian IV of Denmark and Gustavus Adolphus of Sweden in the Thirty Years War were dictated as much by political as by religious ambitions, their decisions to take up arms for the Protestant cause would hardly have been imaginable without their Lutheran upbringing and power bases, as kings of strongly Lutheran states. With regard to Gustavus Adolphus, it is probably more telling that the king chose to wear a black breast plate in battle which proclaimed him to be the champion of God, i.e. Protestantism, than his constant reassurances to the German princes and the emperor that his reasons for intervening in the war were purely political.