What cause the decline of Carolingian empire?

Answer 1

The emperor tried to divide regions of territory out to his sons. These empires did not follow cultural, ethical ties, and did not have local nobility support. This caused the decline of the Frankish empire.

Answer 2

When Charlemagne died, the kings who succeeded him were not capable of wielding reins of power, influential nobles forced these weak successors to give them special rights. These shows the weakness of the central government, that is why the local governments (which had begun to develop during the decline of Rome) again became important

Because the region became disunited, they fell easy prey to new sets of invaders.
The invaders did bad things to towns and churches, but during all these, the central government did nothing to protect its people. :(

After that is the start of Feudalism.

That's the decline of the empire.

Answer 3

Charlemagne ruled the Carolingian Empire. He was also the king of multiple countries; he was King of the Franks and separately King of the Lombards. The land was divided among the king's sons in those days, but Charlemagne only had one son who survived him, so the empire and kingdoms remained intact.

When Charlemagne's son died, one of his grandsons inherited the empire, and both he and the other grandsons inherited separate kingdoms. They had wars with each other, and the authority of the empire gradually declined. For a number of decades, there was no emperor at all.

The imperial title was restored by Emperor Otto I in 962. His empire, however, did not include the Kingdom of the Franks, or France, as it is now called, and is not called the Carolingian Empire, but the Holy Roman Empire instead. The Holy Roman Empire was destroyed by Napoleon about 850 years later.

Many people regard the Holy Roman Empire as the same thing as the Carolingian Empire, and they would say Charlemagne's empire was destroyed by Napoleon. Most historians, however, take the position that Charlemagne's empire fell apart in the wars among his grandsons.