The War of Four Crowns was a defining moment in Idabistani history. It started when the two feuding Britannic nations of Ciaranland and Uenreich fought over domination of Britannia. Their war left a weakness in their nations, and the Katulandic Union declared war to enforce claims on Jorvik in northern Britannia. Britannic possessions in continental Europe came into question and many Idabistani lords wished to see them restored to Idabistani rule. Under pressure by his peers, Napoleon Sebastos declared war on Ciaranland and Uenreich, starting a four-way war between the Katulandic Union, Idabistan, Ciaranland, and Uenreich -- thus, the War of Four Crowns.
The war sparked many notable battles and territorial changes, such as the Idabistani acquisition of Romica and Normandy being added to the Royal Domain of Idabistan Proper . The county of Aubourn was later acquired in another conflict. The war ended with Ciaranland being affirmed as the major power of Britannia. Ciaranland later led invasions against Edgelandt and the Killish and repelled Katulandic attacks. No Britannic nation would ever establish territories in continental Europe ever again.
The war introduced political customs to Idabistan and would lead to Idabistan's first-ever use of conscription in its wars. Infantry troops such as men-at-arms were utilized rather than entire hosts of mounted soldiers. Warfare in Idabistan would be revolutionized by this war and paired with the already militarized government, Idabistan's military was the most skilled for a period of time.