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In 1618, the Thirty Years' War broke out, and John Sigismund himself died the following year. His son, George William, was successfully invested with the duchy in 1623 by King of Poland Sigismund III Vasa, thus the personal union Brandenburg-Prussia was confirmed. Many of the Prussian Junkers were opposed to rule by the House of Hohenzollern of Berlin and appealed to Sigismund III Vasa for redress, or even incorporation of Ducal Prussia into the Polish kingdom, but without success.