Pirenne's points were are summarized in the book's conclusions (the book itself is freely available there) as such

- The Vth century and the fall of Rome in the West didn't put an end to the ancient Mediterranean unity or Roman culture as it existed until the VIIth century : the cultural, economical and political core of Europe was still the Mediterranean Sea and particularly its eastern basin with the Eastern Roman Empire.

- The real, unprecedented, rupture would be found in the Arab conquests over the VIIth and VIIIth centuries, cutting off western Europe from its eastern Mediterranean "motor" except in region taken over by these conquests as Spain was at the cost of their relation with Christian Europe for a time.

- Europeans cores shifted from the South to the North in northern Gaul, Germania, Frisia, England, etc. regardless in trade (Frisian trade network), politics (rise of Carolingians), religion (rise of a Latin Christianity that came to dominate and model a new Christian civilization), etc. bringing the region to a new historical era, the Middle-Ages.

Basically, the Middle-Ages, understood as a Christian, Latin and European civilization would have been a consequence from the rise of Islam and the conquest of the Mediterranean basin forcing western Europe to develop autonomously from the ancient centers and thus break from an ancient Romanity to embrace new times : "Without Muhammad, Charlemagne couldn't have happened".These conclusions and the study themselves, while important and very influential (especially when it comes to the Ecole des Annales) into re-framing the transformations of the post-imperial world into economical, institutional and cultural continuities with the Late Empire which remains a really important focus on the period, were nevertheless heatedly debated since 1935 : but

u/bitparity and u/Tiako provided answers with how much Pirenne's thesis hold or doesn't hold compared to new archeological and historical analysis (with a modest complement there). Essentially, while the Barbarian sustained the Late Imperial momentum, they did so on simpler social-economic basis, becoming the periphery of the post-imperial trade network rather than still participating in it : while they still had access to prestigious eastern Mediterranean goods, most of the exchanges were regional with little export back to the Empire, in a regionalized pattern centered on new political or institutional centers such as aristocratic courts or villae, new hillforts or royal houses in Britain, and eventually monasteries.

The decline of this trade is less clearly observable than thought by Pirenne, with commercial but also economical and institutional changes already happening by the late VIth century : for instance, links with Constantinople were already becoming more distended, possibly due to several factors such as the consequences of Justinian reconquest, Justinian plague, religious disagreements, Romano-Persian wars. Rather than a clear-cut rupture (Carolingian monetary still had a similar silver ratio to Arab coinage, for example), changes issued from the unmistakable political collapse of western Romania gradually happened over what is referred as Early Middle-Ages; on which the Arab conquests would have been "only" a further step, although diversely influential themselves both trough new connections (with the broader European sphere, or locally with communities seemingly "associating" with Saracenic presence and piracy along the Mediterranean shores) and trough reaction to them (inland translation of communities, new centers emerging, etc.).