Why did the collapse of the western roman empire lead to a new age in western europe?

Contrary to the previous answer to this question, Roman culture very much lived on.

As the Western Roman Empire neared its end the Barbarians became "Romanized" in a sense much more than the Romans became "barbarized". That is to say the least once the Western Empire officially fell every barbarian group minus the anglo-saxons took a lot of Roman culture and incorporated it into their own civilizations. The church as well which was the only standing institution left after Rome (an effect of the empire's fall) became the only place where roman culture to the biggest extent was preserved and education as well.

Anyways, now onto the major effects of the fall of the roman empire in Western Europe.

Without any huge empire to "unify" all of Europe the different groups of people became separated and secluded as culturally, militarily, and politically Europe became a giant mess and plunged into what we call the Dark Ages.

The remaining barbarians faced the huge threat of the still living Eastern Roman Empire (Byzantium as Historians have come to refer to it as) not even a few centuries later when Justinian I began a huge conquest of Europe to recreate the Roman Empire. However, an even BIGGER threat to Europe was that without Rome they became very susceptible to invasions from the Muslims (who lo and behold would begin the Muslim conquest which challenged all of the Mediterranean and even wholly took over most of what we know as modern day Spain).

All this being said, the biggest effect of them all as far as I as well as my peers and teachers can conclude is that with no living organisation left it was up to the Church alone to not only preserve much of what was classical learning but also reunify the barbaric tribes under one religion. The church allied themselves with the Franks (they put their money on who they thought was the strongest tribe of them all) and the Franks were able to convert many of the other tribes to Christianity.

The fall of Rome had negative effects like plunging Europe into the Dark Ages but if it hadn't fallen then the Western world we know today could have been very much different country-wise. It also changed Religion forever with the division of Chirstianity into the Catholic and Orthodox down the road (Catholicism vs. Byzantine Christianity). The fall of Rome also led to feudalism which would ultimately end as nations united under monarchies that would slowly evolve into the very political/economical world we see today. Rome was and still is the very thing that I consider to have changed all of the Western world forever.