The Dark Ages of Western Europe began with the collapse of the Western Roman Empire around 400 AD. (Note, however, that the Eastern Roman Empire, based in Constantinople, survived just fine well into the Middle Ages). Islam was not founded until the 7th Century.
There were lots of problems with barbarians, and the Islamic contribution definitely kept things bad for Western Europe for more centuries than would otherwise have been the case.
An interesting aspect to the fall of Rome was that it happened during a Global Cooling period, when dropping temperatures produced lower harvests (and thus less revenue to support the Legions), plus causing mass migrations of barbarian people looking for better farmland.
There are scholars who dispute that. Read Henri Prienne
“Mohammad and Charlemagne” an oldie but goodie.
The central government in Rome may have collapsed, but some of the “barbarian” successor states like the Ostrogoths in Italy and Visigoths in Iberia wished more to carry on in the Roman tradition than to destroy the culture and society. The spread of the Islamic menace through the Mediterranean, along with the kind of endmenic slave-rading and plundering naval actions so typical of Muslim bahavior towards all non-Muslims created a cultural break between western Europe and Byzanitum which was still a bastion of Greco-Roman culture.
“An interesting aspect to the fall of Rome was that it happened during a Global Cooling period, when dropping temperatures produced lower harvests (and thus less revenue to support the Legions), plus causing mass migrations of barbarian people looking for better farmland.”
It may have been a contributing factor in some cases, but the main reason for the initial Volkerwanderung was the conveyor belt of nomad warriors from Central Asia bringing the Huns westward.
The Roman Empire sort of self-destructed due to many factors like the lack of a clear order of secession, which drove a whirlwind of civil wars for imperial control. In the 200’s Roman civil wars pretty much devastated the military leadership of the legions as well as their manpower, driving them to recruit more and more barbarians en mass to fight against their own people under their own leaders rather than to gradually assimilate and Romanize them as they had done earlier. We SHOULD be taking notice of that. Currently, the influx of illegal aliens is so overwhelming our society that our ability to acculturate these people and assimilate them successfully has been seriously compromised, threatening the fabric of our society.