How do you think europe might have changed after the decline of the western roman empire

The period following the fall of the Western Roman Empire in Europe is known as the dark ages. Rome was overran by Germanic barbarians and forests reclaimed many cities and villages. There was a power vacuum as no major empire nor power controlled Western Europe. Some parts of Europe such as Spain, Portugal, and southern France fell to the Umayyads, a Muslim Empire. Meanwhile, diseases such as the Black Plague spread during the latter years of the Dark Ages.

Despite these problems, Europe had relative peace during the Dark Ages. Most wars were small and there were no major conquests, except for Spain as previously mentioned. Life expectancy also increased from 28 during the Roman Empire to 30 during this time, despite the breakout of various diseases.

Feudalism replaced centralized governments in many European countries. Peasants worked the land for lords, and vassals (also called knights) protected the land and the peasants. Meanwhile lords served kings and queens. Feudalism was also an economic system that kept the social hierarchy in tact and prevented any type of social mobility. So poor peasants were unable to move up and become lords.

Christianity spread throughout Europe, with Catholicism dominating Western Europe and Orthodox Christianity becoming the predominant religion in Eastern Europe. Christians waged holy wars known as the Crusades, which invaded Muslim territory and succeeded in capturing Jerusalem, a holy city for all three major Abrahamic religions.  

While the Roman Empire fell in Western Europe, the eastern empire evolved to become a new empire, the Byzantine Empire, which ruled Eastern Europe until 1453 when it fell to the Ottoman Turks.

the answer should be monarchy

which empire had the greatest influence on the history and cultural development of russia?