How was a manor largely self - sufficient both militarily and economically during the early Middle Ages?

Manors were usually consisted of a number of serfs, peasants, artisants, craftsmen and other people each with their own skills that were important for self-sustainability and self-sufficiency during those time. Furthermore, they also possesed a standing army or could recruit soldiers to fight for the lord when it was needed. This is how they ensured self-sufficiency.