The Treaty of Tilsit in 1807 resulted in the Anglo-Russian War (1807–12). Emperor Alexander I declared war on Britain after the British attack on Denmark in September 1807. British men-of-war supported the Swedish fleet during the Finnish War and won victories over the Russians in the Gulf of Finland in July 1808 and August 1809. The success of the Russian army on land, however, forced Sweden to sign peace treaties with Russia in 1809 and with France in 1810, and to join the blockade against Britain. But Franco-Russian relations became progressively worse after 1810, and the Russian war with Britain effectively ended. In April 1812, Britain, Russia and Sweden signed secret agreements directed against Napoleon.