The Swedish Empire or the Great Power era (Swedish: stormaktstiden) was the period in Swedish history spanning much of the 17th and early 18th centuries during which Sweden was a European great power that exercised territorial control over much of the Baltic region. During this period it also held territories on the North Sea and some overseas colonies, including New Sweden. The beginning of the period is usually taken as the reign of Gustavus Adolphus, who ascended the throne in 1611, and its end as the loss of territories in 1721 following the Great Northern War. After the death of Gustavus Adolphus in 1632, the empire was controlled for lengthy periods by part of the high nobility, such as the Oxenstierna family, acting as regents for under-aged monarchs. After its victories in the Thirty Years' War and the subsequent Peace of Westphalia Sweden was granted territories in northern Germany. Sweden reached the height of its power during the Northern War of 1655–1660, when its primary adversary, Denmark–Norway, was neutralized by the Treaty of Roskilde in 1658. Denmark–Norway was forced to give up a third of its territory to save the rest. Although the reign of Charles XII would see initial Swedish victories in the Peace of Travendal (1700) and the Treaty of Altranstädt (1706), he would go on to lead a campaign in Russia that would end in a decisive defeat at the Battle of Poltava. The Russian victory put an end to Sweden's territorial expansion, and by the time of Charles XII's death in 1718 the Empire had been severely diminished both territorially and militarily. Finland was ceded to Russia in 1809, and Sweden's last remaining continental territory (Swedish Pomerania) was ceded to Denmark in exchange for Norway following the Napoleonic Wars. Source: Wikipedia (en)