The United Stormlands
1846 A.D.: The Swedish 1st Artillery begins bombarding Kaupang.
England joins the Roman-Russian War on the side of Russia, breaking its ties to the Swedish-Celtic-Spanish alliance. The Celts publicly denounce Russia to express their disapproval.
Later in the year, Danish berserkers rush across the River of Storms to try and break the enemy lines, and are quickly shot down by Swedish forces.
1847 A.D.: The Danes erect primitive trebuchets, firing them across the River of Storms at the invading Swedes. They fail to inflict significant losses.
1847 A.D.: Kaupang is captured. The Southern Stormland Lords who once ruled it are allowed to keep their holdings as appointed Governor Generals of the Swedish crown. Many of them join with their Northern Stormland counterparts to form the United Stormlands Party, which advocates for a union of all Nordic people under one flag. Supporting this agenda, the Swedish army advances on the Danish city of Aarhus.
Spain makes a declaration of friendship with the defending Danish government, pressured by the Romans on their Northern border. Sweden is once again left with only the loyal Celts to back them.
This is yet another one of those "AI civ, what are you doing?!" moments. I suppose their motive has to be gaining favor with Rome from having declarations of friendship with the same civilizations. Which is understandable, since Rome could pretty much squash them like a bug any time it wants to.