In the Early Modern era, the Baltic Sea was called the Nordic Mediterranean because of its unique outlet on the high seas and its narrowness. Like its southern counterpart, the Baltic is at the crossroads of several peoples and cultures. Also like the Mediterranean Sea, the Baltic had different populations on each of its shores, yet in another way facilitated relations and became a space for interconnections. Throughout its history, peoples from Scandinavia, Poland, Germany, Russia, and the Baltic lands developed not only all sorts of peaceful relations and exchanges, but also competed with each other in long-lasting rivalries or military confrontations. Between the 16th century and the first half of the 19th century, the Baltic region experienced dramatic internal and external changes resulting from its ever-growing connections with the rest of Europe. Baltic issues, however, did not have the same importance for all the surrounding countries: it was the only horizon for Sweden, which enjoyed sovereignty over Finland until 1809, and the main horizon for Denmark, which ruled Norway until 1814. For Scandinavians, the Baltic Sea was a necessary interface for various kinds of exchanges with the external world, whether regional neighbors or continental Europe. In one way or another, the history of the Swedish and Danish kingdoms is interwoven with the history of the Baltic. Scandinavians devoted great attention to this neighboring sea for their shipping and trade, as well as for their security and political influence. The situation is somewhat similar for the Baltic provinces (Estonia, Livonia, and Ingria), which were always under foreign rule, first Swedish then Russian, in the Early Modern period. On the other side of the sea, for the German states, the Polish Republic, and the Russian Empire, the Baltic was simply one theater of foreign policy among others, even though its importance changed over time according to the political or economic context. As for commerce, while during the Middle Ages the Baltic region traded with the rest of Europe, starting in the 16th century, the situation changed as the continental economy shifted from the Mediterranean to the northwest. European population growth and the development of long-distance shipping and commerce meant increasing needs for grain and naval stores. This created new demand for Baltic economic resources and products and for transporting those exports. Consequently, new international rivalries and struggles occurred in the Baltic. At first, these conflicts were among the regional countries, but increasingly the main European powers as well. The Baltic Sea then became an important theater for European international politics, and almost every continental war had a Baltic component. The history of the Baltic Sea from the 16th century to the middle of the 19th century must be considered from two perspectives: first, relations among the regional countries and peoples; and second, relations with the world outside the Baltic, whether foreign powers and regions or even other seas, for political, military, and trade matters.
Ecological variation along the salinity gradient in the Baltic Sea Area and its consequences for reproduction in the common goby
