From 1618 to 1648 Christian princes waged the first pan-European war. Brought about in part by the entrenched passions of the Reformation and Counter Reformation, the Thirty Years War inevitably drew in the Society of Jesus, or Jesuits, who stood at the vanguard of Catholic reform. This book investigates the Jesuits' role during the war at the four Catholic courts of Vienna, Munich, Paris and Madrid and the challenge to the Jesuit superior general in Rome to lead a truly international organisation through a period of rising international conflict. War goals varied and changed at the courts as the conflict progressed. Advocates of 'holy war' contended with moderates, or politiques. This book brings to light the extent to which the Thirty Years War was a religious war and it shows how ideas about the proper relationship between religion and politics shifted under the pressure of events.