This paper discusses the reasons for the decline of the Western Roman Empire and the historical significance of Germany's conquest of the Western Roman Empire.

The decline of the Western Roman Empire was mainly due to internal problems.

First, politically, there is no clear inheritance law under the head of state system.

Second, economically, the most serious economic problems in Rome are caused by slavery and labor shortage.

Third, there is a lack of civic ideals.

The Germans conquered the Western Roman Empire.

Politically, Germanic kingdoms coexist, economically, it is a natural economy, towns decline, and it plays an important role in the manors of Germanic nobles and Roman nobles, as well as the rural communes of Germanic people. Germanic kings did not rule western Europe at all, and they will not rule western Europe. They regard the kingdom as a private manor, and distribute land and power to nobles and priests at will according to their own likes and dislikes. Gradually, Germanic immigrants merged with local residents, Roman nobles married Germanic nobles, and Germanic knights replaced Roman customs. Culturally, Germans are illiterate. The only literate people at that time were priests, and their only spiritual life was in monasteries. The Germanic kings controlled the political power of western European countries, but the leadership of spiritual and cultural life belonged to the Christian church.

This is a dark period, but it is such a period that a new civilization has formed in western Europe, because the unique characteristics of this new civilization have flashed in it: the Christian church can get rid of state power and develop independently to a certain extent, thus producing a unique dual structure of separation of church and state in western Europe. Different from the traditional dual structure in the East, dualism tends to change and innovate. It helps to promote the development of western European civilization. In this way, the tradition of Germanic barbarians and the Roman-Christian culture represented by churches and monasteries are in the process of long-term struggle and integration. It is precisely because of the interaction between Germanic factors and Roman factors that the development of medieval civilization in Western Europe was promoted, thus laying the foundation for the establishment of modern civilization in Western Europe.