1. How was Charlemagne able to maintain such a vast empire?
Charlemagne was able to maintain such a vast empire because from the day he was crowned he had goals to revive and restore the Roman Empire, which he had felt had definitely fallen and needed to be renewed. He reformed cultural, religious, and political life in the empire in order to make the revival a success and to maintain the empire. Reform in all three of these areas was needed because they all interlinked and were important in the day-to-day living of the Romans. Charlemagne also appointed Frankish counts to oversee the conquered lands. He occasionally also sent his own representatives out to spread the word of new laws and such and didn't rely on only written work. He had downfalls in the way his government was run but it was the best that Western Europe had seen up to this point.
2. Why were his successors unable to maintain his empire?
Charlemagne's successors were unable to maintain his empire because the land had been expanded as much as possible under Charlemagne. His son Louis wasn't able to conquer any more lands, which also meant he wasn't able to get the trinkets of war that the nobles were use to being rewarded with. There was a series of problems including nobles turning on each other, Louis's sons fighting and causing civil wars, hostilities between cultural groups flaring up, problems with free peasants being treated unfairly, and breakdowns in trade all helped contribute problems to Charlemagne's successors and eventually led to the breakdown of his once great empire.
3. What countries were formed from the major parts of his empire?
After Charlemagne's death in 814 his empire was descended to his son Louis the Pious. Upon Louis death...