In the beginning of the
Napoleonic Wars,
Denmark–Norway and the
Kingdom of Sweden tried to maintain neutrality but soon became involved in the fighting, joining opposite camps. Swedish king
Gustav IV Adolf entered an alliance with the
United Kingdom of Great Britain and Ireland and the
Russian Empire against
Napoleon Bonaparte in 1805, and declared war on
Napoleonic France. Russia was therein obliged to attack Napoleon's enemies, and since Gustav IV Adolf refused to break his alliance with the United Kingdom, the Tsar invaded
Finland and
severed it from Sweden in the
Finnish War, 1808/1809. In 1812, Napoleon's forces were decimated in their failed attempt to subdue Russia, and started their westward retreat. Sweden allied with Russia on 30 August 1812, with the United Kingdom on 3 March 1813, and with Prussia on 22 April 1813. Previously, on 23 March 1813, she had declared war on Napoleon. When Prussia finally accepted the Swedish claim to Norway on 22 July, Sweden joined the
alliance of Reichenbach concluded between Russia, the United Kingdom and Prussia on 14/15 June. Bernadotte, now free to attack Denmark after Napoleon's
defeat at Leipzig in Mid-October, took his combined Swedish/Russian Army and quickly defeated the outnumbered
Royal Danish Army and occupied
Holstein and
Schleswig during late December 1813. Frederick VI agreed to make peace once it was clear that Bernadotte would occupy
Jutland and
Zealand (with British naval assistance), if necessary to force the Norwegian cession. ==Dano-British treaty==