In what ways did the collapse of the Roman/Mediterranean civilization devastate western Europe?

The collapse of the Roman Empire spurred an invasion of Germanic tribes throughout western Europe. The spread of Christianity through Rome and the division between monotheism and polytheism weakened the internal strengths of the Empire. Once the tribes took power, the population in western Europe dwindled. This was because of the numerous wars and famine that accompanied this new Germanic tribal state.
Another key impact of the fall of Rome was the rise of feudalism. While feudal states did bring some form of consistency to the chaotic life of western Europe after the fall, feudalism ultimately slowed down progress. Feudal states were not able to build like the Roman empire. Moreover, the social structure in the feudal state made it tough for those at the bottom.