While most Europeans (excluding the Jewish communities, the few remaining pagans, and members of heretical groups) may have come to share a religious identity by the eleventh century, Europe was fragmented politically. The numerous Germanic tribes that had dismantled the Western Empire formed the nucleus of the early political units of western Christendom. The Germanic peoples themselves had started as minorities, ruling over formerly Roman subjects. They tended to inherit Roman bureaucracy and rely on its officials and laws when ruling their subjects, but they also had their own traditions of Germanic law based on clan membership.
The so-called “feudal” system of law was one based on codes of honor and reciprocity. In the original Germanic system, each person was tied to his or her clan above all else, and an attack on an individual immediately became an issue for the entire clan. Any dishonor had to be answered by an equivalent dishonor, most often meeting insult with violence. Likewise, rulership was tied closely to clan membership, with each king being the head of the most powerful clan rather than an elected official or even necessarily a hereditary monarchy that transcended clan lines. This unregulated, traditional, and violence-based system of “law” stood in contrast to the written codes of Roman law that still survived in the aftermath of the fall of Rome itself.
Over time, the Germanic rulers mixed with their subjects to the point that distinctions between them were nonexistent. Likewise, Roman law faded away to be replaced with traditions of feudal law and a very complex web of rights and privileges that were granted to groups within society by rulers (to help ensure the loyalty of their subjects). Thus, clan loyalty became less important over the centuries than did the rights, privileges, and pledges of loyalty offered and held by different social categories. Historians refer to that social and political system as "feudalism" or "the feudal system," a hierarchical, class-based structure in which kings, lords, and priests ruled over the vast majority of the population: peasants.
The feudal system was based on a kind of protection system (or even protection racket). A lord accepted pledges of loyalty, called a pledge of fealty, from other free men called his vassals; in return for their support in war he offered them protection and land-grants called fiefs. Each vassal had the right to extract wealth from his land, meaning the peasants who lived there, so that he could afford horses, armor, and weapons. In general, vassals did not have to pay their lords taxes; all tax revenue came from the peasants. Likewise, the Church itself was an enormously wealthy and powerful landowner, and Church holdings were almost always tax-exempt; bishops were often lords of their own lands, and every king worked closely with the Church's leadership in his kingdom.
This system arose because of the absence of other, more effective forms of government and the constant threat of violence posed by raiders. The system was never as neat and tidy as it sounds on paper; many vassals were lords of their own vassals, with the king simply being the highest lord. In turn, the problem for royal authority was that many kings had “vassals” who had more land, wealth, and power than they did; it was very possible, even easy, for powerful nobles to make war against their king if they chose to do so. It would take centuries before the monarchs of Europe consolidated enough wealth and power to dominate their nobles, and it certainly did not happen during the Middle Ages.
One (amusing, in historical hindsight) method that kings would use to punish unruly vassals was simply visiting them and eating them out of house and home - the traditions of hospitality required vassals to welcome, feed, and entertain their king for as long as he felt like staying. Nevertheless, there are many instances in medieval European history in which a powerful lord simply usurped the throne, defeated the former king's forces, and became the new king. Even though the rulership of a given king was always understood to be the will of God, new kings had little trouble arguing that God obviously favored them over the former monarch.
Ultimately, the feudal system represented a “warlord” system of political organization, in many cases barely a step above anarchy. Pledges of loyalty between lords and vassals served as the only assurance of stability, and those pledges were violated countless times throughout the period. The Church tried to encourage lords to live in accordance with Christian virtue, but the fact of the matter was that it was the nobility’s vocation, their very social role, to fight, and thus all too often “politics” was synonymous with “armed struggle” during the Middle Ages.