The war began in 1E 369 following the death of High King Borgas, last living heir of the Ysgramor Dynasty. Borgas was killed during one of the Wild Hunts of Valenwood. The reason for the Bosmer's assassination was that Borgas, a supporter of the Alessian Doctrines of Marukh, had traveled to Cyrodiil to urge the Alessians to launch a joint war on Valenwood. Yet with Borgas' death and no clear heir to the throne, Skyrim was left floundering and leaderless. This marked the end of the First Empire of the Nords.[source?]
Over the years of the Ysgramor Dynasty, the Moot became more partisan and ineffective. The failure of the Moot to appoint the capable Jarl Hanse as Borgas' successor led to civil wars known as the War of Succession. At this time, Skyrim was effectively split down the middle between the Western Holds (Whiterun and Solitude) and the Old Holds (Windhelm and Winterhold).[source?]
The War of Succession caused Skyrim's influence over many of its dominions to wane. The Direnni Hegemony took advantage of the internal strife in Skyrim, and began taking land north and south of High Rock, even claiming portions of Skyrim at certain moments.
In 1E 416, the discord produced by the War of Succession greatly weakened the Nords and caused them to be expelled from Morrowind during the First Battle of Red Mountain (the Second Battle of Red Mountain would occur in 1E 700). The Nords lost all of their territory in Morrowind, and their armies suffered huge casualties at the hands of the combined Chimer-Dwemer army.
In 1E 420, the Skyrim War of Succession ended with the Pact of Chieftans and the crowning of Olaf One-Eye as High King; however, Skyrim had lost the majority of the territory it had earned during the Skyrim Conquests, including High Rock, Morrowind, and a large section of the Nibenay Valley by the time it was all over.