Poland, having lately renewed and firmly established the Catholic religion, was ruled by a King of the Vasa house, who had a legal right to the Swedish crown. She was the leading European power in the East and the standard-bearer of Catholicism against Turks and heretics, and hence a natural enemy of Sweden; and finally she possessed territory and harbors, that had to be brought under Swedish control, if the dream of making the Baltic a Swedish inland sea should be realized by the statesmen at Stockholm. There were therefore various circumstances that might provoke hostilities; but the immediate cause of the war was Sigismund’s pretentions to the Swedish throne, and his continuous refusal to recognize Gustavus Adolphus as the lawful king of Sweden. Gustavus Adolphus therefore determined to attack the enemy in his own country, and in the summer of 1621 he set sail for Riga with a fleet of 148 warships and ten yachts, carrying about 14,000 selected soldiers on board, some being mercenaries from Scotland and Holland. The brilliant campaigns that followed under the King and his able generals arrested the attention of Protestant Europe, and many of the new faith called upon him to become their leader against the Catholics. He expressed his willingness to champion the Protestant cause, and presented a comprehensive plan of operations, while conducting diplomatic conferences with the representatives of England and Holland to the same purpose. But King Christian of Denmark, always jealous of his northern neighbor, also offered his services in the pending struggle and, as his conditions were more moderate and his demands on the allies less exacting than those of Gustavus Adolphus, he was chosen to be the Gideon of the Evangelical Union in its fierce combat with the Catholic League. The Swedish army and navy (both of which had been re-organized and largely increased) were therefore not yet to be used against the imperial forces. Gustavus Adolphus, hoping for more favorable times, went to finish his Polish war, and, after several victorious expeditions through which Sweden gained many advantages and extended her territory, a six years’ truce was concluded at Altmark in 1629.[1]