After Charlemagne died, the Frankish empire fell apart. Without the empire to keep things going, each part of the empire fell to fighting. With each little piece of the empire fighting with each other, some way had to be found to end it. Feudalism grew out of the chaos. Feudalism was a way to get an army together quickly, and it was also a way of life.
Feudalism was a political system. During the Middle Ages, the kings were not very powerful, and there was not one king. There were many kings, each with a territory or land. Since the kings were not powerful, and could not defend their territory effectively, a king divided his lands and gave them to nobles. Nobles were the class next in power. Once the nobles gained land, they divided their land again into smaller pieces called fiefs. They distributed these pieces of land to lower ranking lords of society. These lords were called vassals. There were many, many fiefs in the Middle Ages. Fiefs were awarded for bravery in battle. Others were awarded for other reasons. But all came with a price, a pledge of loyalty.
In order to become a lord with a fief, you had to pledge your loyalty to the noble who gave you your fief, and promise military support in times of need. The fighting men you promised were quite often knights. Feudalism describes the legal obligation of a vassal to a noble, a pledge of support. This political system was called feudalism. It was a way to get an army together quickly to defend a territory.
Under the feudal system everyone served someone above them. A vassal meant some one who serves. The feudal system was based on a pyramid of vassals. Monarchs (Kings) were at the top of pyramid. Lords and Ladies (Nobles) came next, Knights, and at the bottom of the pyramid were Peasants and Serfs. A manor was not a house. It was a unit of land with everything on it, including people, huts, the village, the manor house, and any other buildings or people who lived on that piece of land. The manor was the land and everyuthing on it. A fief was the promise of loyalty to someone above you who gave you the land.
Fiefs: To get a fief (land) and become the head of a manor (the land and everything on it, including people), you had to promise several things.
You had to promise loyalty to the lord (including nobles) who gave you the fief.
You had to promise military service.
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. The vassal system provided that quick access.
Vassals (Nobles) 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. 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. Yet this system existed for hundreds of years.
Manorism was an economic system. The manor was not a house. It was a unit. It included the land and everything on it - the manor house, which was the home of the lord and his family, the peasants, the serfs, their huts, the village, the shops if any, plus any other buildings, people, and animals on the land. Each lord promised the serfs and peasants on his land that he would defend them from attack. In exchange, the serfs and peasants would do all the work - plant, harvest, and make goods for use by the lord and his family, and for themselves. Both sides thought it was a very fair deal. The Middle Ages was an extremely violent time. Lords were always going to war. These lords (vassals) were always being called up to honor their pledge of support. While this was going on, the serfs and peasants took care of the animals, the crops, and production of goods. Peasants did serve, but their pledge did not include military support. They had a job to do and so did the lord of the manor. Peasants could leave the manor if they wished, but where would they go? So they stayed. The serfs went with the land. They had no voice and no choice of staying or leaving at all.
In the absence of central government, the feudal system was a way for people to protect themselves whatever their rank in society, from the lowest serf to the king himself. Feudalism continued to work until the population grew large enough for people to recognize the need for a more centralized government. There was no firm start date and end date of the feudal system, but it started around the 700s CE and ended towards the end of the 1100s CE. The Crusades played a big part in ending feudalism.