Dano-Swedish War (1808–1809)

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.

Source: Wikipedia — Dano-Swedish War (1808–1809) (CC BY-SA 4.0)