Carnthor is the western-most shore of the north of the Iron Empire, and the most important events in human-elf history have occurred there. It was the major fighting ground for the War of the Narrow Sea and the location where the Alliance of Carnthor was signed, as well as where the elves fought their last, losing battle against the Legion on Imperial soil.
Carnthor was invaded by the Damryans at the beginning of the War of the Narrow Sea, chosen predominantly for its advantageous ports. It was seized quickly, the bulk of the Imperial Army tied up fighting Trolls in the east, and claimed as Damryan territory. It was even assigned a Damryan Duke to rule it on behalf of the High Queen Guinnear, and annexed as territory of the Realm. The Realm held it against the efforts of the Imperial Army to reclaim the territory for some fifty years, whereupon elven citizens of the occupied territory rebelled and overthrew the Damryan government.
Since then Carnthor was considered disputed territory, falling into different hands at different times, and was fought over on and off for several centuries. It saw the last official battle of the war when the Imperial Army surrounded and defeated the Realm army, killing High King Shiel and the bulk of Damryan nobility and military officials. The peace treaty with the Realm was signed shortly after and Carnthor again formally fell back under Imperial control.
Less than a hundred years later, Carnthor would again be the site of important events. It was to Carnthor that the elven survivors of the sacking of Leyroth fled, and it was to Carnthor that the eventual aid from the Realm travelled. There was the treaty that formed the Alliance of Carnthor, the agreement to bind together the Realm and the Empire for mutual defence in order to defeat the Legion signed. After being the heart of warfare for centuries, it was at Carnthor that the two sides finally set aside their differences.
It was also at Carnthor that the Alliance fought its first battle, and its first defeat. Despite the unity of humans and elves, many of whom remembered fighting their new allies on this same ground, the Legion overran the army, and drove it across the Narrow Sea. This was the last battle to be fought on Imperial territory, and is the point where the Iron Empire was considered formally lost to the Legion.
Carnthor as a territory had suffered greatly in the War of the Narrow Sea, stripped heavily of resources under Damryan rule and reduced by spending centuries as a battleground. Most of its great ports were destroyed, and it only made sense as the location to which the survivors of Leyroth fled because it had been heavily fortified during and following the war. Otherwise, Carnthor was important by the time it was lost only because of what it represented rather than holding any of its own value.