 Operating off the Barbary Coast, he captured several infamous corsairs and, after negotiating a peace agreement with Salé, De Ruyter returned home May 1656.The same month, the States General, becoming ever more concerned by the expansionary plans of the Swedish king, Charles X, decided to intervene in the Second Northern War by sending a fleet to the Baltic Sea.The Swedes controlled this area after Charles had invaded Poland and claimed the Polish throne.