In Medieval times land was broken up into fiefs. But a fief was more then just a piece of land. A fief had to include at least one village with huts for the serfs, a manor house or castle for the noble, and land to grow or catch food.
A fief was not ownership. A fief was actually a loan from the king and the king could take it back.
Soon fiefs were given to lords and officials. Sometimes fiefs were given as reward for bravery in battle by a lord. Every time two barbarian tribes went to war, the losers lost their land and typically their lives as well. Their families would be kicked out, and their land would be assigned to someone on the winning side. The serfs and peasants and all goods in the manor house or castle would stay with the land. This was one reason war was so popular. War was the way to riches. But it came with a price.
To get a fief (land) you had to promise several things.
You had to promise loyalty to the lord who gave you the fief.
You had to promise military service. Landowners did not have to fight themselves, although most did. But you did have to promise a certain number of knights that could be used in battle for 60 days each year. Some lords would make you promise more than that. Some made you promise that if your lord wanted you to come to his castle for any puny reason, you had to come.
You had to act as a host, providing food and shelter when your lord came visiting.
You had to contribute funds for a ransom if necessary, should your lord be captured in battle.
You had to provide gifts of cash to help offset the cost of your lord's wedding, or any wedding or special occasion of your lord's children.
You had to promise that if you did not keep your promises, you would be tried, convicted, and stripped of your lands. Your family would be kicked out. And your land and its serfs would be awarded to someone else.
In times of trouble, which were often and nearly continuous, a warrior had to have quick access to a large group of fighting men that he could call on for help. These fighters were called vassals.
Vassal means servant. In the feudal system, everybody was a vassal. At the top was the king. At the bottom were the knights. In between were the lords, nobles and officials. Peasants had no real place in the vassal system. They had pledged to do the work on their manor in exchange for protection. The serfs went with the land. They had no voice at all.
Vassals could promise their loyalty to more than one person. You could pledge your support to 10 or 12 lords. But you might have a problem if two or more of your lords went to war with each other. If you didn't keep your promise, your land would be taken away from you. You really couldn't win with this system. If you did not have enough fighting men to protect your land, you would lose a battle, and your land would be taken from you. If you pledged your support to several lords so you would have enough fighting men to protect your land if attacked, you risked two of your lords declaring war on each other. Since you promised both your support, you had to hope you picked the winning side to support to save your lands. Even then, they could be taken from you because you did not keep your word. That would be up to the winning lord.
Being a vassal was taken very seriously. It was not a handshake. There was even a ceremony so that your pledge could be observed by other lords. Small-scale wars and battles were common. Without a strong, central government to act as a control, people were always fighting. There was nothing to stop them. The peasants were not armed. They had no defense. Many fief owners were former warriors. They thought in terms of battle. If they needed more workers, more serfs, they went to war so they could win and get what they needed or wanted. It was a time of intense and continuous violence.
The Church tried to limit these battles. They kept passing decrees, like no fighting in church. They passed decrees that said no fighting on holidays or weekends. Finally, the church made fighting legal on only 80 days a year. It did a little good, but not much. The church had no army. They had no way to enforce the decrees. Private wars continued to savage Western Europe.
What happened if you chose not to participate in the this system? You'd just rather not have land at all. What would happen to you? You could join the church if they would have you. You could become a peasant. A peasant thought it was pleasant to be a peasant. Not the life for you? So what would you do? There was nothing else. There were only three groups of people in the Middle Ages - the common people, the church, and the nobility. There were no towns until late in the Middle Ages. There was no middle class, no fast food, no malls, no television, no computers, no cell phones, no internet, and no radios - there was only war.