The Last War was fomented by a succession dispute over the throne of Galifar.
King Jarot had five heirs, each governing one of the Five Nations: Mishann of Cyre, Thalin of Thrane, Wrogar of Aundair, Wroann of Breland, and Kaius of Karrnath. Mishann was the eldest child and therefore had the legal claim to the throne; though her brother Thalin tried to persuade Jarot that Mishann was too weak to rule, the old king maintained tradition. Jarot gave Mishann his blessing on his deathbed, and exacted a promise from Wrogar to support his sister’s right to the throne.
After Jarot’s death, his children gathered at the island of Thronehold for the funeral and succession ceremony. Thalin, however – supported by Wroann and Kaius – outright rejected Mishann’s claim to the throne. It soon became obvious that each of Jarot’s heirs would use the armies of their nation to back up their side of the dispute. All of Jarot’s children left Thronehold with the dispute unresolved. Shortly thereafter, the first clashes of the Last War broke out.
The war raged for a century. Not every nation was heavily involved in the fighting at every point in time, but all were affected by the war. Territory, even whole cities, were captured and lost, and new nations were carved from the flanks of Aundair, Karrnath, Breland, and Cyre by treachery, rebellion, or diplomacy.
Only the utter devastation of Cyre on the Day of Mourning four years ago, it seemed, sufficed to bring the warring descendants of Jarot’s heirs to their senses. The war cooled immediately, hesitant peace talks began a few months later, and two years after Cyre’s annihilation, the nations of Khorvaire convened at Thronehold once more and signed a treaty that both ended the war and cemented the political shape of the continent. The peace is fragile, and few believe in their hearts it will last for long, but it is holding still.