The academic institutional theory for the advent of the Dark Ages in Europe is that Barbarian hordes invaded Europe and dumbed down the civilization. Yes, this had a small effect, along with a mini Ice Age, but the truth is that Muslims created the European Dark Ages. The European Dark Ages were dark because of the dark economic shadow of the Islamic control of the Mediterranean Sea during that time period. Muslim pirates ended European sea trade to the Middle East and Far East through the Mediterranean Sea. Following a basic principle that if you cut off trade, a civilization declines in all areas of life. This is why Muslims attacked the World Trade Center of the United States of America on 9/11. Diminish a civilizations economy, and their ability to defend themselves or counter attack is decreased.