In the early years of the seventeenth century, the Holy Roman Empire of the German people had the misfortune to be the centre of intense internal and international rivalries. The authority of the emperor, Diet and imperial courts had broken down, and there could be no settlement by peaceful means of conflicting claims to territory and title. Protestant princes feared the loss of church lands secularized after 1552; the return to the Roman Catholic church of bishoprics, abbeys, cloisters and countless parishes also meant the enforced re-Catholicization of the populations involved. Since the Donauwörth affair of 1608, not even an imperial city could feel safe in the worship of its choice. The very existence of a defensive Protestant Union confronted by an armed Catholic League was a menace to peace. While the great majority of German princes were peace-loving, sometimes at the risk of their security, a few were ready to seize any opportunity to increase their territories and to enhance their prestige.

If there was danger of chaos and civil war, foreign entanglements posed an even greater threat. England and the United Provinces (the Dutch) were members of the Protestant Union. The marriage of the Elector Palatine of the Rhine to the daughter of James I added to England's interest in Germany. In the north there were further foreign involvements. The king of Denmark was also duke of Holstein, a prince of the empire with claims on secularized bishoprics. His ambition to control the Baltic coast was, in turn, challenged by the king of Sweden.