During the Middle Ages, peaceful trading gradually gained the upper hand over piracy and conquest. From the Italian cities the wares of the south and the Orient came over the passes of the Alps and down the German rivers, where trading cities grew up to act as carriers of merchandise and civilization among the nations of the north. The merchant guilds of these cities, banded together in the Hanseatic League, for at least three centuries dominated the northern seas.
Perhaps the most extensive commercial combination ever formed for the control of sea trade, the Hanseatic League began with a treaty between Lübeck and Hamburg in 1174, and at the height of its power in the 14th and 15th centuries it included from 60 to 80 cities, of which Lübeck, Cologne, Brunswick, and Danzig were among the chief. The league cleared northern waters of pirates, and used embargo and naval power to subdue rivals and promote trade. It established factories or trading stations from Nishni Novgorod to Bergen, London, and Bruges. From Russia it took cargoes of fats, tallows, wax, and wares brought into Russian markets from the east; from Scandinavia, iron and copper; from England, hides and wool; from Germany, fish, grain, beer, and manufactured goods of all kinds. The British pound sterling (Österling) and pound avoirdupois, in fact the whole British system of weights and coinage, are legacies from the German merchants who once had their headquarters in the Steelyard, London.
In the early 15th century the league attempted to shut Dutch ships from the Baltic trade by restricting their cargoes to wares produced in their own country, and by coercing Denmark into granting the league special privileges on the route through the Sound. This policy, culminating in the destruction of the Dutch grain fleet in 1437, led to a naval struggle which extended over four years and ended in a truce by which the Dutch secured the freedom of the Baltic. It was a typical naval war for sea control and commercial advantage, in which the Dutch as a rule seem to have got the better, and in which the legend first made its appearance of a Dutch admiral sweeping the seas with a broom nailed to his mast.
From this time the power of the Hansa declined. This was partly because the free cities came more and more under the rule of German princes with no interest in, or knowledge of, commerce; partly because of rivalry arising from the union of the Scandinavian states (1397) and the growth of England, France, and the Low Countries to national strength and commercial independence; and partly also because of the decline of German fisheries when the herring suddenly shifted from the Baltic to the North Sea. Underlying these varied causes, however, and significant of the far-reaching effect of changing trade-routes upon the progress and prosperity of nations, was the fact that, when the Mediterranean trade route was closed by the Turks, and also the route through Russia by Ivan III, the German cities were side-tracked. Antwerp and Amsterdam were not only more centrally located for the distribution of trade, but also much nearer for Atlantic traffic--an advantage which Germany has ever since keenly envied.