The Battle of the Frontier was the name given by historians to a series of skirmishes between the Fel Empire and the Ssi-ruuvi Imperium before the Second Imperial Civil War. The Ssi-ruuvi incursions into the Outer Rim Territories began when the Elders' Council, dominated by the ambitious High Elder Nis'k, wanted to enlarge the Imperium's territory through expansion. The battles between the forces of the Empire, which was ruled by the Fel dynasty at the time, and the Imperium were initially either indecisive or victories for the Ssi-ruuvi.
However, in 124 ABY, the Imperium suffered a major defeat at the Battle of Zaddja, taking such heavy losses that they could not launch a major offensive into Imperial space again. However, minor skirmishes between border patrols occurred at the edge of the Unknown Regions between Imperial and Ssi-ruuvi ships until the beginning of the Ssi-ruuvi Civil War in 130 ABY.