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The term for people who surrendered their land to a lord in return for protection was "vassal." Vassals would promise loyalty and military service to the lord in exchange for the use of the land.
vassals. Vassals were appointed by a lord to protect him in exchange of land.
Land held by a feudal lord was known as a "fief" or "feudal estate." This land was granted to the lord by the king or a higher-ranking noble in exchange for loyalty, military service, and other obligations. The lord could then grant smaller portions of the land to vassals in return for their loyalty and service.
It was in exchange for an oath of loyalty.
fight for the king and serve them 2nd Answer: To expand that a bit, when a greater noble (was not always a king) granted land to a vassal the vassal could take on a number of responsibilities, including military service, hospitality for the lord and his servants, attendance of the lord's court to give advice and council, and participation in the lord's entourage. In the later middle ages the demands for physical military service could sometimes be converted to a monetary payment. This was known as scutage.
When knights offered their service to the king in return the king would give them land.2nd Answer: A knight did not always hold his land from a king. In many cases, it would be from another feudal lord, such as a Duke, Baron, Earl, etc. But the basic idea above is correct. The greater lord gives the knight a manor from his land holdings. This manor provides income for the knight. In return the knight owes military service. This could be actual service in war, or it could be a number of days spent each year in the garrison of a castle.In the later middle ages the military service was sometimes converted to a cash payment, with which the greater lord could hire soldiers or mercenaries. This cash payment was known as scuttage.In general a vassal might be asked to do other things for his lord as well, such as providing hospitality for the lord or his agents, participation in the lord's entourage, or attendance of the lord's court to provide advice and council.
Land held in return for duty or service to a lord.
A vassals duties were to serve a lord of a higher rank and to keep faith and loyalty to the lord against all others.
In return for protection and the fief, the vassal did service for the lord. He had to pay homage to his lord and pay dues. The most important service was military service as a knight: military expeditions, standing guard or letting the lord use the vassal's own caslte. This relationship made it possible for the lord to build up armies and to rule over a territory with large warrior groups of vassals.
A person who serves a lord is typically referred to as a vassal or a servant. They provide assistance to the lord in various capacities, such as managing land, providing military service, or attending to the lord's needs.
Political allegiance and providing military, political, and financial service to a lord. More at LINK