Gustavus’s situation, at his accession, was critical. The King of Poland laid claim to his dominions, and Denmark and Muscovy were in arms against him. The danger was most pressing on the side of Denmark; and thither Gustavus’s first efforts were directed. But in Christian IV. he had to contend with an able enemy, from whom he gained no advantage; and after one unsuccessful campaign he accommodated the quarrel at the expense of some concessions. In the war with Muscovy he was more fortunate; and he reduced the Czar to purchase peace in 1617, by the sacrifice of the provinces which border the Gulf of Finland and the Baltic sea. During these years of warfare, Gustavus found leisure to bestow attention upon internal improvements. He devoted much thought and care upon strengthening the Swedish navy, esteeming that to be his surest defence against invasion; he sought to encourage commerce; he purified the administration of justice, by rendering judges less dependant upon the crown, and by abridging the tediousness and expense of lawsuits; and he laboured to devise means for increasing the revenue by judicious arrangement, without adding to the burdens of the people. Both in peace and war he received the most valuable assistance from his zealous, faithful, and sagacious minister, the celebrated Oxenstiern. In 1620 Gustavus travelled incognito through the chief towns of Germany. At Berlin he formed acquaintance with Maria Eleonora, sister to the Elector of Brandenburg, whom he espoused at Stockholm in November of the same year. One daughter, the famous Christina, his successor, was the offspring of this marriage.