Anglo-Swedish war of 1810–1812

During the Napoleonic Wars until 1810, Sweden and the United Kingdom of Great Britain and Ireland were allies in the war against Napoleon. As a result of Sweden's defeat in the Finnish War and the Pomeranian War, and the following Treaty of Fredrikshamn and Treaty of Paris, Sweden declared war on the UK. The bloodless war, however, existed only on paper, and the UK was still not hindered in stationing ships at the Swedish island of Hanö and trade with the Baltic states.

Source: Wikipedia — Anglo-Swedish war of 1810–1812 (CC BY-SA 4.0)