Why did the Charlemagne's empire break up after his death?

Charlemagne's empire fragmented after his death in 814 due to a combination of weak leadership and internal divisions among his heirs. His grandsons, who inherited the empire, struggled to maintain control over the vast territories and faced challenges from external threats and internal revolts. The Treaty of Verdun in 843 further formalized the division of the empire into three separate kingdoms, leading to the eventual decline of centralized authority and the rise of localized powers. This fragmentation set the stage for the development of modern European nations.