What you are discussing is the Pirenne Thesis, the product of two late 19th century economic historians Henri Pirenne ()Belgian) and Alfons Dopsch (Austrian). The current promoter of this thesis is Michael McCormick (Harvard). A synopsis by Bryce Lyon,
The Middle Ages in Recent Historical Thought, Washington, American Historical Association, 1965,
http://teaching.arts.usyd.edu.au/history/1025/sect4/pirennelyon.html
the essential characteristic and lifeblood of the Roman Empire - its unity and coherence, resting upon control of the Mediterranean from the Bosphorus to the Strait of Gibraltar. For centuries the Mare Nostrum of the Romans had been the cement that held firm the great imperial structure; over its waters had passed trade and commerce, the Roman military and naval might, and the vital exchange of ideas.
German kingdoms
had no effective political ties with the eastern half of the Empire, they had still partaken of the Mediterranean unity and had enjoyed unbroken economic exchange with the East.(3)
The Arab conquest destroyed this Mediterranean rapport; political, economic, and cultural exchange ended. Except for the most tenuous of ties between Constantinople and a few Italian ports the Arabs had rolled down an iron curtain between East and West that remained down until the eleventh century.
The West which had always been parasitical, drawing upon the superior economic resources of the East, reverted to an agrarian economy or, as Pirenne said, to "an economy of no outlets."
Perinne's two major works are:
Economic and Social History of Medieval Europe (New York, 1937).
Mohammed and Charlemagne (New York, 1939)