Mieszko I
Cooperation with Sweden and the war against Denmark

Probably in the early 980s Mieszko allied his country with Sweden against Denmark. The alliance was sealed with the marriage of Mieszko's daughter Świętosława with the Swedish king Erik. The content of the treaty is known from the traditional account—not entirely reliable, but originating directly from the Danish court—given by Adam of Bremen. In this text, probably as a result of confusion, he gives instead of Mieszko's name the name of his son Bolesław:

Mieszko decided on the alliance with Sweden probably in order to help protect his possessions in Pomerania from the Danish King Harald Bluetooth and his son Sweyn. They may have acted in cooperation with the Wolinian autonomous entity. The Danish were defeated c. 991 and their ruler was expelled. The dynastic alliance with Sweden had probably affected the equipment and composition of Mieszko's troops. Perhaps at that time the Varangian warriors were recruited; their presence is indicated by archaeological excavations in the vicinity of Poznań.
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