He's referring (at least in part) to the so-called "Pirenne Thesis", first proposed in 1937 by Belgian historian Henri Pirenne in his book "Muhammad and Charlemagne". Pirenne proposed that the Germanic successor states of Rome were continuing the same level of economic and cultural activity as the old centralized Roman system, and that it wasn't until the Arab Muslim armies conquered the eastern and southern shores of the Mediterranean, which is what (he claimed) actually cratered the European economy and sparked the Dark Ages.
His thesis was considered pretty fringe and was rejected by other historians at the time, and modern archaeology has only confirmed that view (for a good contemporary overview of the thesis and why it's wrong, see "The Pirenne Thesis: Analysis, Criticism, And Revision", and for the modern perspective, "Mohammed, Charlemagne, and the Origins of Europe: Archaeology and the Pirenne Thesis", both available on Amazon).
This thesis was revived in recent years by crackpot pseudohistorian Emmet Scott (the main English-language promoter of Heribert Illig's bizarre Phantom Time Hypothesis, which claims that the years 614 AD to 911 AD never actually existed and that all the people and events in them were the result of a grand medieval forgery...the fact that Illig's thesis completely contradicts Pirenne's does not seem to bother Scott one bit), in his "Mohammed and Charlemagne Revisited".
The thesis has been latched onto by modern Islam-haters, because it portrays Muslims as civilizational destroyers and the reason why the Dark Ages happened (which, naturally, they see as a warning for today), which is why Skydive5 talks about it.
EDIT: A glowing review of Scott's book was even published at FrontPageMag...written by none other than Anders Breivik's hero Fjordman!
