In the years 1648–1653 the Brandenburg Hohenzollerns achieved the long-desired goal of their foreign policy: they got a direct access to the sea, but commercial benefits were rather scarce without the Oder estuary and Szczecin (Stettin). So they fought on until they managed to conquer the whole of the missing territory in 1720. It created completely new possibilities for the development of maritime trade. A selective mercantilism, with its specific Prussian tinge, was to assuage the fact that the country was divided into three economic parts. The priorities of the first economic sector and the home trade were the reasons why in that historic moment Prussia was not able to join the mainstream of the Baltic maritime trade because of the weakness in capital of the merchants and the poor quality of the Prussian craft and manufactured goods, which were sold only in the East. Until 1740 Prussia had a negative balance in its foreign trade, and in its exports there was mainly agricultural and forest produce. The merchants from the Prussian ports limited themselves to the agency between European shipowners and their own ports’ surroundings, excluding Silesia as the Oder trade was not competitive at all compared to the Elbe region. The army and the finance were the political priorities for Frederick II (1744– 1797), as it had been for his father. Yet, he achieved his economic objectives thorough a variety of methods and means. He wanted to reach a positive balance in foreign trade, in which maritime exchange played a role that was much more important than before, and which became the main priority of his economic policy, at least up to 1806, although after 1786 that policy was being implemented with less and less determination. A logical consequence of such a policy was a doctrine according to which it was advisable to harm your neighbour as much as possible, which led to trade and customs wars against Saxony, Austria and Poland. The conflict with Poland was especially acute, which after 1772 Frederick changed into a colonial receiving market. In order to achieve a positive trade balance Prussia used protectionism, oversea colonial trade, and an increasing participation of the Prussian ports in the Baltic and European trade. Altogether, it caused that at the end of Frederick II’s reign the surplus of Prussia’s foreign trade reached the level of 5 million talers. In the exchange the maritime trade had a more and more weight. At the turn of the 18th and 19th centuries the biggest Prussian ports were: Gdańsk (Danzig) and Szczecin (Stettin), and – to a lesser degree – Królewiec, Elbląg and Kłajpeda.