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 years of existence connected to the White Sea through Karelia due to the isostatic depression caused by the ice sheet of the earlier Saalian ice age. Little is known about the Baltic Sea during the oscillations of the Weichselian ice age, the last glaciation. The first Weichselian glaciations, corresponding to MIS 5b and 5d, penetrated parts of the Baltic Sea depression from north to south but did not got south beyond the Åland Islands. The Weichsel ice sheet reached northern Denmark about 65–60 thousand years ago. When the last ice sheet began to retreat north from the Baltic Sea depression