What was exchanged between lords and vassals?
At its core, it was an agreement between a lord and a vassal. A person became a vassal by pledging political allegiance and providing military, political, and financial service to a lord. A lord possessed complete sovereignty over land, or acted in the service of another sovereign, usually a king.
What was exchanged between serfs and lords?
In exchange for tending a lord’s demesne, a serf could expect the lord’s private army to protect them. The lords needed the serfs, too; labor shortages caused by war and disease limited the available workforce in Western Europe.