When Sweden went to war
Sweden and Norway had a union since the negotiated peace in Kiel 1814.
This was an unhappy union for Norway, as their national identity suffered under Swedish rule and Norway decided one sidedly to sesede from the union in 1905.
This has many similarities with the ongoing crisis in Ukraine, and there is much to learn from this story. Today for many Swedes it is unthinkable that Swedish soldiers mobilised to wage a war against our brother nation, but to the world it was a situation that always ended in war.