How did the feudal countries in Western Europe come about?

First of all, you must know that European history from the fall of the Western Roman Empire in 476 to about 1500 is called the "Middle Ages" by Western historians. This is the period between the demise of ancient Greek and Roman civilization and the emergence of modern capitalist society. a period of history. Chinese historians call it the feudal society of Western Europe. After the fall of the Western Roman Empire, the Germans established several states on its territory. Among them, the Frankish Kingdom developed into a major country in Western Europe. During the reign of Charles, the Frankish kingdom reached its peak. In 800, Charlemagne's empire was established. In 814, Charles died. His descendants were mediocre and incompetent, fighting against each other, and the country fell into chaos. In 843, they divided the empire into three parts. Later, from these three parts, three feudal countries, France, Germany and Italy, respectively developed. In the mid-5th century, during the migration wave of the Germanic people, the Anglo, Saxon and other tribes among them entered Britain from the European continent and established some small countries. After a long period of annexation, these countries began to form the unified Kingdom of England in the early 9th century. However, in these Western European countries, political development has been tortuous and difficult, the country has been fragmented for a long time, and unified centralized rule emerged only very late. It was not until the 15th century that Britain and France established a unified centralized state by strengthening the royal power and cutting off the power of the great feudal masters. The situation in Germany was even worse. East Francia, which split from Charlemagne, gradually developed into the German Kingdom. The German King Otto I was ambitious and expanded into Italy. With the support of the Pope, he established the so-called "Holy Roman Empire" in the 10th century. However, because the emperor's power was restricted by feudal lords and the pope, the empire was in vain. In the following hundreds of years, the princes in the empire became so powerful that they did not take the emperor seriously. By the 14th century, there were still seven vassal states in the empire, which were in a state of separatist rule. During a long historical period, Germany had numerous checkpoints, inconvenient transportation, and frequent feudal melees. Until the mid-19th century, Germany still had dozens of small states, which were in a state of fragmentation, and a unified centralized state could not be established for a long time. In the 1860s and 1970s, Prussia, the most powerful among them, unified Germany and established a military autocratic rule with a strong feudal character. The situation in Italy is basically the same as that in Germany, which has been in a state of feudal division for a long time.