The primary economic system in Europe during the Middle Ages was feudalism. This system was characterized by a hierarchical structure where lords owned vast tracts of land and vassals or serfs worked the land in exchange for protection and sustenance. The lord-vassal relationships formed the basis of political and social organization, with land as the main source of wealth and power. The economy was largely agrarian, and trade existed but was limited compared to later periods. Overall, feudalism defined the medieval European social and economic structure until its gradual decline, giving way to more modern systems.