Indeed, Mahan emphasized the utility of blockade as it was executed during the American against the Confederate ports in order to stop all exports of cotton to Europe and the supply of food and equipment to the South. This has been well apprehended by the British during the First World War when the Royal Navy carried out a naval blockade since 1914 to stop the maritime supply of Germany and its allies. It is seen as a key element in the final victory of the allies. The North Sea was declared a war zone in November 1914 and the ships entering it did so at their Risks and perils. The blockade was so restrictive that even food products were considered "smuggling war". By 1915, German imports had already fallen by 55% compared with the pre-war
