The guiding policy of James I, as King of England and the acknowledged leader of Protestant Europe, had been since his accession one of rapprochement with the great Catholic powers. To this end he had determined to marry his son and heir, Prince Charles, first to a Bourbon, and then a Hapsburg princess. James saw himself not as the leader of a bloc, but as a mediator impartial in the interests of peace. To his mind this was the most exalted function of Christian kingship, and it was his hope that Spain and England, the leaders of Christendom's two camps of faith, could preserve the peace of Europe by acting in concert.
Yet James was no dreamer. While courting Spain, he retained hegemony among his fellow Protestants. If he proposed to marry Charles to a Catholic, he had matched his daughter Elizabeth to a Calvinist, the Elector Palatine Frederick V. The latter alliance, however, was to prove to be his fatal mistake, for it sucked him inextricably into the maelstrom of German politics and precipitated not only the gravest foreign crisis of his reign, but a domestic one of ultimately far greater significance as well.
Frederick was the leader of the most important alliance of Protestant powers in Germany, the Evangelical Union. He was also one of the seven electors who chose the Holy Roman Emperor. Three of these were Catholic bishops, three secular Protestants, and the last, the King of Bohemia, had for a hundred years been the emperor-designate himself, to wit, the senior male representative of the House of Hapsburg. It was evident, therefore, that any disturbance in the orderly succession to the Bohemian crown would immediately jeopardize the traditional Hapsburg claim to the imperium, and with it the entire European balance of power.