The Finnish War (, , ) was fought between the Kingdom of Sweden and the Russian Empire from 21 February 1808 to 17 September 1809 as part of the Napoleonic Wars. As a result of the war, the eastern third of Sweden was established as the autonomous Grand Duchy of Finland within the Russian Empire. Other notable effects were the Swedish parliament's adoption of a new constitution and the establishment of the House of Bernadotte, the new Swedish royal house, in 1818. Background After the Russian Emperor Alexander I concluded the 1807 Treaty of Tilsit with Napoleon, Alexander, in his letter on 24 September 1807 to the Swedish King Gustav IV Adolf, informed the king that the peaceful relations between Russia and Sweden depended on Swedish agreement to abide by the limitations of the Treaty of Tilsit which in practice meant that Sweden would have been required to follow the Continental System. The king, who viewed Napoleon as the Antichrist and Britain as his ally against Napoleon's France, was apprehensive of the system's ruinous consequences for Sweden's maritime commerce. He instead entered into negotiations with Britain in order to prepare a joint attack against Denmark, whose Norwegian possessions he coveted. In the meantime, the Royal Navy attacked Copenhagen and the Anglo-Russian War (1807–1812) was declared. Referring to the treaties of 1780 and 1800, the emperor demanded that Gustav Adolf close the Baltic Sea to all foreign warships. Although he reiterated his demand on November 16, 1807, it took two months before the king responded that it was impossible to honor the previous arrangements as long as the French were in control of the major Baltic ports. King Gustav Adolf did this after securing an alliance with Britain on 8 February 1808. Meanwhile, on 30 December 1807 Russia announced that should Sweden not give a clear reply Russia would be forced to act. Although most Swedish officers were skeptical about their chances in fighting the larger and more experienced Russian army, Gustav Adolf had an unrealistic view of Sweden's ability to defend itself against Russia. In Saint Petersburg, his stubbornness was viewed as a convenient pretext for Russia to occupy Finland, thus pushing the Russo-Swedish frontier considerably to the west of the Russian capital and safeguarding it in case of any future hostilities between the two powers. The situation was problematic for Sweden, since it once again faced both Denmark and