The Dano-Swedish War of 1808–1809 was a war between Denmark–Norway and Sweden due to Denmark–Norway's alliance with France and Sweden's alliance with the United Kingdom during the Napoleonic Wars. Neither Sweden nor Denmark-Norway had wanted war to begin with but once pushed into it through their respective alliances, Sweden made a bid to acquire Norway by way of invasion while Denmark-Norway made ill-fated attempts to reconquer territories lost to Sweden in the 17th century. Peace was concluded on grounds of status quo ante bellum on 10 December 1809.
During the War of the First Coalition Denmark-Norway and Sweden had remained neutral. The two Nordic countries also intended to follow this policy during the War of the Second Coalition and had in 1800, together with Prussia and Russia, formed the Second League of Armed Neutrality in order to protect their merchant fleets from the British policy of unlimited searches of neutral shipping for French contraband. The League would however, be dissolved following the Battle of Copenhagen and the death of Tsar Paul I of Russia in 1801. After the collapse of the alliance, and Denmark-Norway's brief war with Britain, Sweden and Denmark still continued their policy of neutrality.
In 1805 Sweden joined the war against France, but following the rapid French advance through northwest Germany and the defeat at Lübeck, Swedish forces had to withdraw to Swedish Pomerania. Attempts at peace negotiations between France and Sweden was initiated, and Emperor Napoleon I of France offered Sweden in the autumn of 1806, Norway in exchange for Swedish Pomerania. But the negotiations failed, and in early 1807 French forces invaded and eventually occupied Swedish Pomerania.
Following the Treaties of Tilsit in 1807 the main focus of France and Britain was directed towards Denmark. Napoleon wanted to include the neutral Denmark-Norway in the Continental System while the United Kingdom feared that the Danish fleet should fall into the hands of the French. British forces bombarded and occupied Copenhagen, capturing most of the Danish navy. Denmark-Norway subsequently allied with France, but without a navy the Danish could do little.
The alliance between Denmark-Norway and France was signed at Fontainebleau on 31 October 1807. The agreement indicated vague promises from the French that they would help Denmark-Norway regaining its fleet, while Denmark had to commit themselves to participate in an eventual war against Sweden together with France and Russia. Crown Prince Frederik of Denmark-Norway was reluctant to participate in war against Sweden, but he decided to declare war against Sweden with the aim of conquering the territory which Denmark-Norway had lost after the Treaty of Brömsebro and Treaty of Roskilde.
Since Sweden's attention was on Finland following the Russian invasion in February 1808, he saw it as easier to take back the territories. On 14 March 1808 the Danish Minister in Stockholm presented the declaration of war to the Swedish government, and the Swedish king, Gustav IV Adolf replied with planning an invasion of Sjælland, in order to force Denmark to conclude separate peace. This plan was however, temporarily sidelined and the Swedish troops in Götaland were instead placed in a defensive position, following rumors that Napoleon had sent reinforcements to Denmark. King Gustav IV instead approved the plan drawn up by Gustaf Mauritz Armfelt, on an invasion of Norway to compensate for a possible loss of Finland.
The Swedish army stationed in Sweden counted a total of 23,000 men, 7,000 in southern Sweden under the command of Count Johan Christopher Toll, 14,000 towards the Norwegian border under the leadership of Gustaf Mauritz Armfelt, and 2,000 in Norrland under Johan Bergenstråhle.
The Swedish army was fairly well equipped and the soldiers were well trained, but under the pressure from two fronts the Swedes had been forced to retain the ability to send troops wherever they were needed the most. The main theater of war was in the east, where the Russian invasion threatened the Swedish rule in Finland, but the threat from Denmark–Norway and France was taken seriously. The Swedish western army was divided into two wings, the right wing was led by Armfeldt himself, and the left wing was led by Major General Vegesack.
The army's right wing furthermore consisted of Colonel Carl Pontus Gahn's "Flying Corps" of approximately 650 men in Dalby, Colonel Leyonstedt's 1st Brigade of approximately 1,600 men in Eda, Colonel Schwerig's 2nd Brigade of about 2,500 men in Töcksmark, Colonel Bror Cederström's 3rd Brigade of approximately 1,750 men in Holmedal, and Colonel Johan Adam Cronstedt's 4th Brigade of approximately 1,700 men in the area east of Marker. The army's left wing consisted mainly of one brigade at Strömstad, one at Töftedal and one in the area between Gothenburg and Uddevalla.
The Danish-Norwegian army combined consisted of 36,000 men. The Danish army could muster 14,650 men, but only 5,000 of them could be used for attacks against the Swedish. The Norwegian army had been prepared for a future war with Sweden since the fall of 1807, but since they had diverted resources for coastal protection duties along the long Norwegian coast, it was in a poor state in late February 1808. The Norwegian army ended up with a lack of weapons, ammunition, clothes, food and many soldiers had equipment that was close to 20 years old.
The Norwegian army was under the leadership of Prince Christian August of Augustenburg who at that time was President of the Norwegian Government Commission, which had been established when the Royal Navy had initiated a naval blockade between Norway and Denmark in 1807. Christian August would later during the war also be appointed Governor-general of Norway.
24 dragoon companies totalling about 1,800 riders
14 musketeer battalions (each with 4 divisions) for a total of about 8,400 men
10 sharpshooter companies totaling about 1,200 men
10 depot battalions (each with 3–4 divisions) for a total of about 5,000 men
8 grenadier battalions (each with 4 divisions) for a total of about 4,800 men
6 fortress batteries totaling about 300 men
3 Field batteries (1 and 2 mounted marching batteries) totaling approximately 300 men