text: Foreign policy King James I was sincerely devoted to peace, not just for his three kingdoms but for Europe as a whole. He called himself "Rex Pacificus" ("King of Peace"). Europe was deeply polarized, and on the verge of the massive Thirty Years' War (1618–1648), with the smaller established Protestant states facing the aggression of the larger Catholic empires. In 1604, James made peace with Catholic Spain, and made it his policy to marry his daughter to the Spanish prince. The marriage of James' daughter Princess Elizabeth to Frederick V, Elector Palatine at Whitehall 14 February 1613 was more than the social event of the era; the couple's union had important political and military implications. Across Europe, the German princes were banding together in the Union of German Protestant Princes, headquartered in Heidelberg, the capital of the Palatine.  King James calculated that his daughter's marriage would give him diplomatic leverage among the Protestants. He thus would have a foot in both camps and be able to broker peaceful settlements.  In his naïveté, he did not realize that both sides were playing him as a tool for their own goal of achieving destruction of the other side. The Catholics in Spain, as well as the Emperor Ferdinand II, the Vienna-based leader of the Habsburgs who controlled the Holy Roman Empire, were both heavily influenced by the Catholic Counter-Reformation.  They had the goal of expelling Protestantism from their domains.