For the remaining years of his reign until 814, Charlemagne's campaigns were limited. He mostly remained in his palace at Aachen. Still, having been crowned Emperor, his relations with Constantinople were awkward, in that Byzantium was slow to recognize him as a Western imperial colleague. Thus, through 813, Frankish forces made inroads on the declining Byzantine possessions in the Adriatic and in Italy, until Emperor Michael I sent emissaries prepared to recognize the Carolingian as basileus, emperor. In September of that year, he had his son Louis the Pious crown himself Emperor.
The last decade of Charlemagne's rule was not as accomplished as his earlier years. His key concerns were establishing Carolingian succession and the division of lands amongst his sons. He had three, for whom he designed a plan in 806. According to the Divisio Regnorum, Pepin was to keep enlarged Lombard lands; Louis was to receive an augmented Aquitane as well as southern and western areas, while Charles, the oldest son, was to get traditional Francia--Austrasia and eastern conquests, as well as Neustria. By 811 Charles' and Pepin's deaths made the arrangement irrelevant. Louis was now to receive all. Finally, foreboding future events, in addition to entanglements with Andalusian Muslims in the 800-806 period, first hostile encounters with the Vikings took place in 808-810, when the Danish King Godefred raided Frankish Frisia and clients' areas north of the Elbe.
Louis the Pious succeeded his father as sole ruler of Francia in 814. In 816, he had himself re-coronated by Pope Stephen IV, setting a precedent that all claimants to emperorship would follow. The first fifteen years of his reign were divided among three concerns: 1) dealing with continuing military matters, now in a defensive manner. Slavs beyond the Elbe and in the Northwest Balkans were fought off, while Lombard duchies in southern Italy were repeatedly disciplined. Likewise, Bulgars who had wandered west were pushed off, just as constant skirmishes with the Arabs in the Marches were meant to protect Barcelona. 2) Appropriate to his epithet, Louis was intensely concerned with religious matters in his realms. He wanted a Christian kingdom. This began by enforcing religious morality in his palace, encouraging princesses to enroll in nunneries. He also held ecclesiastical councils at Aachen in 816-817, under the influence of his close adviser Wittiza, known as St. Benedict of Aniane. In the next years, they wold insist that all monasteries adopt the Benedictine Rules. Further, he insisted that high Church prelates in his realms become quasi- monastic in conduct. They should be 'regular' as opposed to 'secular' clergy. Benedict's 821 death only decreased the aggressiveness of the program. 3) Like his father, Louis faced the insurmountable succession-division dilemma. Wanting to preserve the territorial unity of Francia, his idea in the 820s was to give the great majority of the kingdom to his oldest son Lothair, with much smaller regions going to Charles the Bald and Louis the German. Naturally Charles and Louis the German were disappointed, and spent the next twenty years in fratricidal strife.
Between 829 and 833, Louis the Pious was twice deposed as ruler and then reinstated by warring sons. Only a balance of fear kept him in power for the rest of the decade, and on his death in 840 his two younger sons Charles and Louis combined to fight Lothair. The Battle of Fontenoy's losses were tremendous, yet the results required compromise. Charles the Bald received the western regions from forty miles east of Paris to the southwestern Marches and stretching from the English Channel to the Mediterranean. Louis the German received eastern districts from the Marches beyond the Elbe to just outside Strasbourg, and from Denmark in the north to the Adriatic in the south. Wedged in between this was Lothair's kingdom, stretching from the North Sea all the way past the papal States in Italy, with the Imperial capitals. Accordingly, it was he who received title of emperor. While Charles' and Louis' shares approximate to the divisions of France and Germany, the middle kingdom was so unstable that it was divided amongst Lothairs' three sons at his death in 855. When the inheritor of the northern region dead in 869, Charles the Bald and Louis the German both tried to seize it. With the exception of Italy and Provence the middle kingdom was thus eliminated, igniting civil wars between an embryonic France and Germany that continued into the tenth century.
The Carolingian Empire is remembered as the first truly glorious Medieval polity in Europe. With Charlemagne's creation of a single state out of a massive swath of Italian and Gallic lands; his assumption of title of Holy Roman Emperor through coronation by the Pope; and keen interest in Christianity's progress, it is plausible to view a reemergence of the unity of ethos and purpose which characterized the Roman state six-hundred years before. Still, as we recall that the Carolingians were no more than another Frankish clan like the Merovingians, whose evolving power was based on conquest and usurpation of authority from kings, we must ask: what differentiated Charlemagne's state from that of his predecessors, and how did it exhibit substantial similarities? Further, when looking at the Carolingian decline from the 820s onwards, what insoluble dilemmas, or problems of political technology, doomed these states?
Charlemagne was not a political innovator, and did not provide any new sort of political glue to a polyglot, multi-traditioned state. Mostly, the administration of his domains was based on the Merovingian pattern of dependence on counts, whose loyalty was sought by dint of the King's raw power, and the benefits to be derived from association with him. Beyond that, the Churh was incorporated more closely into administration, as had been the trend from Pepin onwards. On the militarized borders and in newly conquered areas, margraves, or border counts, were established to maintain order, defend new acquisitions, and support the conversion process. A small group of the king's associates watched over all of this, and were in frequent contact with Charlemagne at Aachen. The King's sons were made titular kings of newly acquired areas, with some limited executive power. The challenge of this whole system was not unlike that in the Merovingian period--how to guarantee the continued loyalty of local administrators. There was no mechanism to do so, and often Charles' army was the answer. Additionally, missi dominici were royal agents created by Charlemagne. Consisting of a lay noble and a cleric sent directly from the palace out to the counties, they were to convey the king's desires and report back to him the conditions of the realm. As long as--and only as long as--a powerful king stood behind the missi, the system could work. As well, though the right of localities and various ethnic groups to individual customary law codes was recognized, during Charlemagne and Louis the Pious' lifetime, capitularies were issued by the central government which applied to all subjects equally. Finally, yearly assemblies were held in the spring or summer. Gathering together counts, dukes, their retinues, and the royal host, issues of general concern would be addressed, after which the army would go off to fight across the nearest border. As far as fiscal administration was concerned, public taxation was not much more orderly than it had been under the effective Merovingians. Aside from certain dues, the king lived mostly off the revenues of his large estates scattered throughout Francia. Moving from one to another as provisions ran low, it allowed him to check up on conditions regionally. All in all, "we are still dealing with a primitive German monarchy--but a primitive German monarchy presided over by a political genius" quite adept at warfare.