The First Messenian War was a war between Messenia and Sparta. It began in 743 BC and ended in 724 BC, according to the dates given by Pausanias. The war continued the rivalry between the Achaeans and the Dorians that had been initiated by the Return of the Heracleidae (Dorian Invasion). Both sides utilized an explosive incident to settle the rivalry by full-scale war. The war was prolonged into 20 years. The result was a Spartan victory. Messenia was depopulated by emigration of the Achaeans to other states. Those who did not emigrate were reduced socially to helots, or serfs. Their descendants were held in hereditary subjection for centuries until the Spartan state finally needed them for defense.