Claim: Swedish Empire was ruled by Gustav II Adolf for 21 years.

The Swedish Empire -LRB- stormaktstiden , `` the era of great power '' -RRB- refers to the Kingdom of Sweden 's territorial control of much of the Baltic region during the 17th and early 18th centuries , a time when Sweden was one of the great European powers . The beginning of the Empire is usually taken as the reign of Gustavus Adolphus , who ascended the throne in 1611 , and the end as the loss of territories in 1721 following the Great Northern War . In Swedish history , the period is referred to as stormaktstiden , literally meaning `` the Great Power era '' .   After the death of Gustavus Adolphus in 1632 , the empire was , over lengthy periods , controlled by part of the high nobility , most prominently the Oxenstierna family , acting as tutors for minor regents . The interests of the high nobility contrasted with the uniformity policy -LRB- i.e. , the upholding of the traditional equality in status of the Swedish estates favoured by the kings and peasantry -RRB- . In territories acquired during the periods of de facto noble rule , serfdom was not abolished , and there was also a trend to set up respective estates in Sweden proper . The Great Reduction of 1680 put an end to these efforts of the nobility and required them to return estates once gained from the crown to the king . Serfdom , however , remained in force in the dominions acquired in the Holy Roman Empire and in Swedish Estonia , where a consequent application of the uniformity policy was hindered by the treaties by which they were gained .   After the victories in the Thirty Years ' War , the climax of the great power era was reached during the Second Northern War , when their primary adversary Denmark was neutralized by the Treaty of Roskilde in 1658 . However , in the further course of this war as well as in the subsequent Scanian War , Sweden was able to maintain her empire only with support of her closest ally , France . Charles XI of Sweden consolidated the empire and ensured a period of peace , before Russia , Saxony and Denmark started a concerted attack on his successor , Charles XII . After initial Swedish victories , Charles secured the empire for some time in the Peace of Travendal -LRB- 1700 -RRB- and the Treaty of Altranstädt -LRB- 1706 -RRB- , before the Battle of Poltava -LRB- 1709 -RRB- finally brought the great power era of Sweden to an end .