The Treaty of Andaria was a treaty signed by the four demonic hordes--the Eastern Horde, the Northern Horde, the Southern Horde and the Western Horde--to conclude their rivalry at the end of the Second Great War and begin building what became known as the Andarian Empire after the Dissolution of Libaterra at the dawn of the Fourth Age. The demons' power had weakened and their numbers had diminished in the aftermath of the war, which prompted them to sign the treaty for an indefinite ceasefire so they could focus their efforts on controlling the lands they had already conquered and strengthen them against future opposition both within and without. This decision put a halt to the demons' expansionistic plans and ushered in a time of relative peace for the first two decades of the Fourth Age.
The signing of the Treaty of Andaria and the founding of the Andarian Empire is commemorated as a nationwide public holiday called Empire Day.