These conflicts formed part of a longer struggle for dominance in the area which can be traced back to the advance of the Germanic peoples into eastern Europe in the early Middle Ages, driving the Slavic inhabitants further and further along the southern coastline until they were largely cut off from the sea. Colonization was accompanied by the establishment of trading posts to tap the rich hinterlands. Such towns came together under the lead of Lübeck to form the eastern branch of the great Hanseatic League which dominated the region’s economy from the end of the thirteenth century.1 Against such German dominance the Scandinavian kingdoms of Denmark, Norway and Sweden formed the Union of Kalmar at the end of the fourteenth century. Of this Denmark, with its command of the entrance to the Sea, its wealth and its strong fleet, was the leader and the prime contender to enforce the doctrine of mare clausum or the right to exclude the ships of all nations which lay beyond it. It was also Denmark who first asserted the principle (if not in so many words) of dominium maris Baltici, an assertion of sovereignty over at least the Baltic between the Danish islands and the eastern coast of the Sea.2 The clash between the League and the Union was complicated by rivalries within the latter which led to its eventual breakup in the 1520s, leaving Denmark and Norway united and a suspicious Sweden-Finland fearing the forced reimposition of control from Copenhagen.