Swedish – Norwegian War ( 1814 ) The Swedish - Norwegian War , also known as the Campaign against Norway ( ) , or the Norwegian Campaign ( ) ; was a war fought between Sweden and Norway in the summer of 1814 . The war resulted in Norway entering into union with Sweden , but with its own constitution and parliament . Background . Treaty of Kiel . As early as in 1812 , prior to the Napoleonic invasion of Russia , the Swedish Crown Prince Charles John had entered into an agreement with Tsar Alexander I that Russia would support a Swedish attack on Norway in order to force Denmark - Norway to cede its northern part to Sweden . The Swedish attack against Norway was rejected , however , and Swedish forces were instead directed against France in Central Europe . The Swedish troops were deployed against Napoleon ' s forces as a result of agreements between Charles John and diplomats from the United Kingdom and Prussia , which indicated that Norway would be ceded to Sweden after France and its allies ( which included Denmark - Norway ) were defeated . By the Treaty of Kiel in January 1814 , King Frederik VI of Denmark - Norway had to cede Norway to the King of Sweden , due to Denmark - Norway ' s alliance with France , and its defeat during the later phases of the Napoleonic Wars . This treaty was however not accepted by the Norwegians . The Norwegian Constituent Assembly . Prince Christian Frederick of Denmark , heir presumptive to the throne of Denmark and Governor - general of Norway , took the lead in the insurrection , and he called for a constitutional assembly . This adopted the liberal constitution of 17 May , which also elected Christian Frederick as the king of an independent Norway . As the head of the new state , Christian Frederick desperately tried to gain support from the United Kingdom , or any of the other major powers within the Sixth Coalition , in order to maintain Norway ' s independence . However , the foreign diplomats gave no hope for any outside support to the Norwegians . Armies . The Norwegian Army mustered 30 , 000 men , and it had taken up positions away from the border with Sweden , in the fear of being outflanked . The Norwegian navy had few vessels , and most of them were stationed at the islands of Hvaler , close to Sweden . The Swedish Army consisted of 45 , 000 men , experienced and well - equipped soldiers . The Swedish Navy had a number of large vessels and a capacity for moving and landing troops . War . The hostilities opened on 26 July with a swift Swedish naval attack against the Norwegian gunboats at Hvaler . The Norwegian army was evacuated and the vessels managed to escape , but they did not take part in the rest of the war . The main Swedish offensive came across the border at Halden , bypassing and surrounding the fortress of Fredriksten , and then continuing north , while a second force of 6 , 000 soldiers landed at Kråkerøy outside of Fredrikstad . This town surrendered the next day . This was the start of a pincer movement around the main part of the Norwegian army at Rakkestad . On the front towards Kongsvinger the forces were more evenly matched , and the Norwegian army eventually stopped the Swedish advance at Lier on 2 August , and won another victory at Matrand on 5 August . On 3 August , King Christian Frederick reached the front at Østfold and was persuaded to change his strategy and use the 6 , 000 men stationed at Rakkestad in a counterattack against the Swedes . The order to counterattack was given on the 5th of August , but the order was recalled a few hours later . The Norwegian forces therefore withdrew over the Glomma river at Langnes in Askim . The last major battle of the war was fought on 9 August at the bridgehead at Langnes , where the Swedish forces once more were driven back . Although the Norwegian Army had won at Langnes , it was nevertheless clear to both the Norwegian and Swedish military authorities that a defeat was inevitable . Even as they had managed to deliver several minor offensive blows to the Swedes , thus applying pressure on the Swedes to accept Norway as a sovereign nation , it was considered impossible to try to stop the Swedes in the long run . The Swedish offer of negotiations was therefore accepted as the war had put a heavy strain on the Norwegian finances . Every day of delay in securing Norway by the Swedes brought uncertainty to them regarding the outcome , so both parties were interested in a quick end to the war . For the ordinary Norwegian soldier the war had seemed ill - prepared and ill - fought , the allegations of the loss were against Christian Frederick and the Norwegian general Haxthausen ; the latter was accused of treason . For the Norwegian government it probably had been more of a matter of getting the best possible bargaining position , as without the support of major powers Norway ' s independence was impossible to secure . But by agreeing to talks following the victory at Langnes they were in a situation where they could avoid an unconditional surrender . Aftermath . Negotiations started in Moss , Norway on 10 August 1814 , and after a few days of hard negotiations , a cease fire agreement , called the Convention of Moss , was signed on 14 August 1814 . King Christian Frederick was forced to abdicate , but Norway remained nominally independent within a personal union with Sweden , under the Swedish king . Its Constitution was upheld with only such amendments as were required to allow it to enter into the union , and the two united kingdoms retained separate institutions , except for the King and the foreign service and policy .