The Swedish–Norwegian War was a war fought between Sweden and Norway in the summer of 1814. According to the Treaty of Kiel, Norway would enter a union with Sweden under Charles XIII of Sweden. The war resulted in Norway being forced into the United Kingdoms of Sweden and Norway, but with its own constitution and parliament. The war marked the last time Sweden participated in an armed conflict with another nation until 2011, and its conclusion signalled the beginning of the country's long period of military neutrality.