The empire of Charlemagne turned out to be a political failure. After the emperor's death his dominions were divided. Further, a wave of invasions occurred. The year 845 witnessed the burning of Hamburg and the sack of Paris by the Northmen or Vikings, while in 847 Bordeaux suffered a like fate. The Frankish empire was ultimately split into five kingdoms, frequently engaged in war with one another. Meanwhile the Saracens were invading Italy and nearly captured Rome.
We see two forces arrayed against the Carolingian Dynasty: one internal, the failure to plan an orderly succession which would keep the empire unified; one external, the Muslim Saracens whose Islamic armies would attack Italy, Sicily, and along the Mediterranean coastline from Spain to Greece.
A third force destabilized society: the corruption and destabilization of the Church. Long a center of learning - the monasteries of the early Middle Ages housed the sum of Greco-Roman classical wisdom and literature - and a center of social support - food, clothing, vocational training, and employment were offered freely to those in need - the Church was infiltrated by those who were interested neither in rational reflection nor in social welfare. Pretending to embrace the Christian faith, these spies insinuated themselves into the Church's structure and spread their unchristian activities from within:
The Church fell victim to exploitation by the new feudal nobility. Abbacies and bishoprics were sued as rewards for laymen or unworthy prelates; and in the tenth century the papacy itself was under the control of local nobles and factions. In such circumstances the educational movement inaugurated by Charlemagne could not be expected to bear much fruit.
It would be decades before the intellectual engine of Europe would reach peak operating power again: but when it did, the Scholastic philosophers of the High Middle Ages would lay the groundwork for modern chemistry and physics as they turned human reason's attention both to nature and to the mind's own processes.