The feudal system flourished in the High Middle Ages. While it had its origins in the centuries after the collapse of the western Roman Empire, the formal system of vassals pledging loyalty to kings in return for military service (or, increasingly, in return for cash payments in lieu of military service) really came of age in the eleventh and twelfth centuries. The lords themselves presided over a rigidly hierarchical social and political system in which one’s vocation was largely determined by birth, and the vocation of the nobility was clearly defined by landowning and making war.
Lords - meaning land-owning nobles - lived in “manors,” a term that denoted not only their actual houses but the lands they owned. All of the peasants on their lands owed them rent, originally in the form of crops but eventually in cash, as well as a certain amount of labor each year. Peasants were subdivided into different categories, including the relatively-well off independent yeomen and freeholders, who owned their own plots of land, down to the serfs, semi-free peasants tied to the land, and then the cottagers, who were the landless peasants worse-off even than serfs. The system of land-ownership and the traditional rights enjoyed by not just lords, but serfs and freeholders who lived under the lords, is referred to as “manorialism,” the rural political and economic system of the High Middle Ages as a whole.
One of the traditional rights, and a vital factor in the lives of peasants, were the commons: lands not officially controlled by anyone that all people had a right to use. The commons provided firewood, grazing land, and some limited trapping of small animals, collectively serving as a vital “safety net” for peasants living on the edge of subsistence. Access to the commons was not about written laws, but instead the traditional, centuries-old agreements that governed the interactions between different social classes. Eventually, peasants would find their access to the commons curtailed by landowning nobles intent on converting them to cash-producing farms, but for the medieval period itself, the peasants continued to enjoy the right to their use.
The kingdoms of Europe up to this point were barely unified. In many cases, kings were simply the most powerful nobles, men who extracted pledges of loyalty from their subjects but whose actual authority was limited to their personal lands. Likewise, kings in the early Middle Ages were largely itinerant, moving from place to place all year long. They had to make an annual circuit of their kingdoms to ensure that their powerful vassals would stay loyal to them; a vassal ignored for too long could, and generally did, simply stop acknowledging the lordship of his king. Those patterns started to change during the High Middle Ages, and the first two kingdoms to show real signs of centralization were France and England.
In France, a series of kings named Philip (I through IV) ruled from 1060 to 1314, building a strong administrative apparatus complete with royal judges who were directly beholden to the crown. The kings ruled the region around Paris (called the Île-de-France, meaning the "island of France"), but their influence went well beyond it as they extended their holdings. Philip IV even managed to seize almost complete control of the French Church, defying papal authority. He also proved incredibly shrewd at creating new taxes and in attacking and seizing the lands and holdings of groups like the French Jewish community and the Knights Templar, both of whom he ransacked (the assault on the Knights Templar started in 1307).
In England, the line descending from William the Conqueror (following his invasion in 1066) was also effective in creating a relatively stable political system. All land was legally the king’s, and his nobles received their lands as “fiefs,” essentially loans from the crown that had to be renewed for payments on the death of a landholder before it could be inherited. Henry II (r. 1154 – 1189) created a system of royal sheriffs to enforce his will, created circuit courts that traveled around the land hearing cases, and created a grand jury system that allowed people to be tried by their peers.
In 1215, a much less competent king named John signed the Magna Carta (“great charter”) with the English nobility that formally acknowledged the feudal privileges of the nobility, towns and clergy. The important effect of the Magna Carta was its principle: even the king had to respect the law. Thereafter English kings began to call the Parliament, a meeting of the Church, nobles, and well-off commoners, in order to get authorization and money for their wars.