wismar was occupied by a coalition of danish, prussian, and hanoverian troops during the great northern war of 1700–1721. this resulted in the destruction of the city's elaborate defence system. after the treaty of frederiksborg ended the war, wismar was returned to swedish control. however, since sweden had lost several nearby possessions (such as bremen-verden) to its rivals, wismar began to lose significance as it became more of an outpost of swedish control rather than the center of a larger hub.