History of the North Sea great herring fishing industry resulting in Scotland becoming a European leader in that industry. During the First Schleswig War (1848–51), the Crimean War (1854–56) and the Second Schleswig War (1864), belligerents took steps to reduce or eliminate commerce in the North Sea by their enemies. In the first Schleswig War, Denmark was able to halt maritime commerce by Germany in the North Sea and in the second, imposed tolls on ships crossing through the Danish straits between the Baltic and North Seas. The Crimean War saw British and French expeditions sent into the Baltic to prevent Russian ships' egress into
Geology of the Baltic Sea in the early Holocene (ca. 10,000 years ago) glacier meltwater accumulated between the front of the ice sheet and the southern shores that were free of glacier ice. This accumulation of freshwater constituted a lake known as the Baltic Ice Lake. This lake did not mix with seawater from the west because the ground on the whole depression rose faster than sea level did. Eventually mixing and connection to the ocean did occur when the glacier front retreated to the north beyond Billingen about 11,500 years ago. The Baltic Ice Lake drained then rapidly reaching sea level. From this point