Why did Charlemagne need to declare the Frankish state an empire?

Why did Charlemagne need to declare the Frankish state an empire? What did it give him. What states did the empire of Charlemagne split into? Why did this happen?

The declaration of the Frankish kingdom as an empire gave some privileges to its government. After the name was changed, the status of the state changed. During the reign of Charlemagne, the Frankish Empire reached a high level in the development of trade and craftsmanship. The empire began to seize foreign markets for goods. The Frankish state disintegrated into separate parts, because Charlemagne bequeathed to his sons various territories, which in the future developed independently. This is how modern states appeared in Europe.