Dominium maris baltici The establishment of a ( " Baltic Sea dominion " ) was one of the primary political aims of the Danish and Swedish kingdoms in the late medieval and early modern era s . In the struggle for the " dominium maris baltici " ( Northern Wars ) , the Danish and Swedish navies played a secondary role , as the dominium was to be won through control of key coasts by land warfare . Etymology . The term , which is commonly used in historiography , was probably coined in 1563 by the king and grand duke of the Polish - Lithuanian union , Sigismund II Augustus , referring to the hegemonial ambitions of his adversaries in the Livonian War . The first written reference stems from the Dutch - Swedish treaty of 5 ( O . S . ) / 15 ( N . S . ) April 1614 , concluded in The Hague . Wars over the Baltic . The Baltic sea was vital for many European powers . It was a source for important materials , and a growing market for many commodities . The importance of the region was such that it was of interest even to powers that did not have direct access to it , such as Austria and France . For several centuries , Sweden and Denmark would attempt to gain the total control of the sea , a policy that was opposed by other local and international powers . The control of the Baltic has been described as one of the main goals of the Denmark ' s and Sweden ' s policies . The conflict over the Baltic was heavily shaped by the expansionist policy of the Scandinavian ( Nordic ) powers , who sensed opportunity in the power vacuum created by the weak or non - existent naval power of the Holy Roman Empire and Poland - Lithuania . Denmark and Sweden used their control of parts of the Baltic to fuel their militaries . Both claimed the Baltic as theirs , and promised to protect foreign shipping . While the Nordic powers vied with one another over control , they both agreed that it should be the domain of one of them , not an " outsider " , like Poland or Russia . The Scandinavian powers tried to prevent the rise of the opposition through diplomatic treaties , in which other powers like Russia or Germany were forbidden to create their navies , and through military actions , whether targeting opponent naval forces , or through taking control of the Baltic ports . In one of the most notable actions to retain its monopoly over the Baltic , Denmark destroyed , without declaration of war , the nascent Polish - Lithuanian Commonwealth Navy in 1637 . The numerous wars fought for the dominium maris baltici are often collectively referred to as Northern Wars . Early on , Denmark had the upper hand , but eventually , it lost to Sweden . Neither Denmark nor Sweden managed to realize thorough military and economic control of the Baltic , though Sweden during her time as an empire came closest to that aim before the Great Northern War . Danish " dominium maris baltici " . In historiography , the term " dominium maris baltici " is used either in a narrower sense as a new Swedish concept of the Early Modern era , closely tied to the Swedish Empire , or in a wider sense including the preceding Danish hegemony in the southern Baltic Sea . Dernmark had subdued the southern Baltic coast in the 12th century , but lost control in the 13th century after her defeat in the Battle of Bornhöved ( 1227 ) , with the exception of the principality of Rügen . Thereafter , the Hanseatic League became the dominant economic power in the Baltic Sea . Valdemar IV " Atterdag " of Denmark is credited by Robert Bohn as the first Danish king pursuing a policy of establishing a Danish " dominium maris baltici " , aiming at adding to Denmark ' s naval dominance an economical hegemony at the expense of the Hanseatic League . To achieve this aim , Valdemar sold Danish Estonia to the Teutonic Order state in 1346 , consolidating his finances and raising an army from the revenue . After initial territorial gains , Valdemar conquered the Hanseatic town of Visby ( Gotland ) , resulting in a war decided by the League in the peace of Stralsund in 1370 , which marked the climax of Hanseatic power . Atterdag ' s daughter and " de facto " successor , Lady Margaret , managed to concentrate the crowns of Denmark , Norway and Sweden in her Copenhagen - centered Kalmar Union . In 1429 , Kalmar king Eric of Pomerania started to raise the Sound Dues from merchants entering or leaving the Baltic Sea , allowing the Copenhagen court to benefit from the Baltic Sea trade profits without engaging in economic adventures itself . The Sound Dues , imposed until 1857 and constituting a primary source of income for the Royal treasury , quickly became a contentious issue which brought Denmark in conflict with the Hanseatic League and the neighboring powers . After the break - up of the Kalmar Union , the Kingdom of Sweden became Denmark - Norway ' s primary rival for hegemony in the Baltic Sea . Christian IV of Denmark ' s victory in the Kalmar War in 1613 marked the last instance of a successful defense of the " dominium maris baltici " against Sweden , while the subsequent wars ended in favor of the latter . The period of Danish intervention in the Thirty Years ' War ( " Kejserkrig " ) is also considered part of the wars for the " dominium maris baltici " — in this war , however , the opponent was not the Swedish king , but the ambitious Holy Roman Emperor Ferdinand II , who temporarily planned to establish the empire as a naval power in the Baltic . He assigned this task to Albrecht von Wallenstein , leading to a concerted action of Denmark and Sweden in the defense of Stralsund . The Danish defeat in the battle of Wolgast and the subsequent treaty of Lübeck in 1629 however removed Denmark from the battlefield . Swedish " dominium maris baltici " . After Sweden had become independent from the Kalmar union , she became Denmark ' s major rival for the " dominium maris baltici " . The first war ascribed to this conflict is the Northern Seven Years ' War ( 1563 – 1570 , associated with the Livonian War ) , between 1611 and 1613 followed the above mentioned Kalmar War . Major Swedish successes followed the capture of Riga in 1621 and the Swedish landing in Pomerania in 1630 . The gains in the Torstenson War , a theater of the Thirty Years ' War , humiliated Denmark , and the subsequent Peace of Westphalia confirmed Sweden ' s status as a European great power ( " stormaktstiden " ) . Swedish control of the Baltic was not thorough , however , since the Maritime Powers , especially Dutch Republic , continued to be economically and militarily present and pursued their balance of power policy also in respect to Denmark and Sweden . The Second Northern War , the Scanian War and the first stage of the Great Northern War left Sweden ' s " dominium maris baltici " intact , yet it was finally ended by the Treaty of Nystad in 1721 . Sweden had sought to secure her " dominium maris baltici " by turning many towns ( e . g . Riga , Narva , Wismar ) into fortresses , often under the aegis of Erik Dahlberg . Since the Thirty Years ' War , Sweden collected customs ( " Licenten " ) from merchant vessels on the Baltic Sea , in Swedish as well as in non - Swedish ports . These customs were calculated as a certain percentage of the value of transported goods , and once payment took place in any port , the respective receipt was valid for the whole " dominium maris baltici " . Aftermath . The failure of the Scandinavian powers to take control of the Baltic , and steadfast refusal of other powers – local and international – to recognize their claims , is seen as one of the factors that led to the development of the " freedom of the seas " principle in the international law .