It set out an alternative argument about the end of Roman influence in Europe and the emergence of the Dark Ages which emphasised the importance of the Arab expansion in the Middle East and Levant which has become known as the Pirenne Thesis.

Although successive historians have tended to reject the argument as an explanation of the period, it remains influential as a means of thinking about geography and periodisation in the Early Middle Ages and the debate it sparked is widely taught in university medieval history courses.

The two articles began a lengthy scholarly debate among historians, and Pirenne sought to explore further aspects of the subject in the body of studies later compiled into the book.

Islamic conquest of the area of today's south-eastern Turkey, Syria, Palestine, North Africa, Spain and Portugal ruptured economic ties to Western Europe and cut the region off from trade and turning it into a stagnant backwater, with wealth flowing out in the form of raw resources and nothing coming back.

Instead, the Muslim conquest of North Africa made the Mediterranean a barrier; cut Western Europe from the east; and enabled the Carolingians, especially Charlemagne, to create a new distinctly-western form of government.