Winter in the North Sea was always shrouded in fog. Sometimes the westerly winds blew it inland, turning cities like Amsterdam into "fog cities." Visibility fell below ten meters, and even streetlamps looked blurred and indistinct.
The North Sea had originally been a bay on the eastern edge of the Atlantic Ocean, where the Rhine River had once flowed. As glaciers carved through the land during the Ice Age, mountains were washed away, ultimately leaving a shallow basin between England and the continent. Compared with the Atlantic Ocean, the North Sea was relatively shallow. Its seabed deposits consisted mainly of glacial gravel, sand, and silt, redistributed by currents and waves.
The tides of the North Sea were complex. The tidal range offshore was only one meter, while along parts of England's coast it reached seven meters. When heavy waves combined with storm surges, the damage to coastal areas became even more severe, sometimes throwing up waves more than ten meters high.
Yet compared with the Netherlands, England still possessed many excellent harbors, such as Liverpool. Economically, the northerners of the Netherlands were far ahead of the southerners, thanks to their coastal dikes. Amsterdam, Rotterdam, and The Hague became internationally renowned major ports, built their own maritime trading fleets, and could trade with Germany along the Rhine River. The southern Netherlands, meanwhile, was hemmed in by mountains, lacked mineral resources, had not established its own merchant fleet, and imported eighty percent of its raw materials from France. Its economy was comparatively underdeveloped.
The Netherlands had originally belonged to Middle Francia. After its king died, his descendants began fighting over the inheritance. The country fragmented, and the feudal lords went to war. In 1384, the Duchy of Burgundy occupied all the land. After Charles the Bold died, the duchy was divided between