Between the years of 1560 and 1658, Sweden created a Baltic empire centred on the Gulf of Finland and comprising the provinces of Karelia, Ingria, Estonia, and Livonia. During the Thirty Years' War Sweden gained tracts in Germany as well, including Western Pomerania, Wismar, the Duchy of Bremen, and Verden. During the same period, Sweden conquered Danish and Norwegian provinces north of the Sound (1645; 1658). These victories may be ascribed to a well-trained army, which despite its comparatively small size, was far more professional than most continental armies, and also to a modernization of administration (both civilian and military) in the course of the 17th century, which enabled the monarchy to harness the resources of the country and its empire in an effective way. Fighting in the field, the Swedish army (which during the Thirty Years' War contained more German and Scottish mercenaries than ethnic Swedes, but was administered by the Swedish Crown[18]) was able, in particular, to make quick, sustained marches across large tracts of land and to maintain a high rate of small arms fire due to proficient military drill.
However, the Swedish state ultimately proved unable to support and maintain its army in a prolonged war. Campaigns on the continent had been proposed on the basis that the army would be financially self-supporting through plunder and taxation of newly gained land, a concept shared by most major powers of the period. The cost of the warfare proved to be much higher than the occupied countries could fund, and Sweden's coffers and resources in manpower were eventually drained in the course of long conflicts.
The foreign interventions in Russia during the Time of Troubles resulted in Swedish gains in the Treaty of Stolbovo (1617). The treaty deprived Russia of direct access to the Baltic Sea. Russian fortunes began to reverse in the final years of the 17th century, notably with the rise to power of Peter the Great, who looked to address the earlier losses and re-establish a Baltic presence. In the late 1690s, the adventurer Johann Patkul managed to ally Russia with Denmark and Saxony by the secret Treaty of Preobrazhenskoye, and in 1700 the three powers attacked.
