How Did Charlemagne Unwittingly Unleash a New Round of Invasions

Multiple Choice

How did Charlemagne unwittingly unleash a new round of invasions into his realm before his death?

A) He insisted that neighboring states acknowledge him as emperor of the Western world.
B) He sent Christian missionaries into the pagan kingdoms of his neighbors.
C) He destroyed the buffer states around his kingdom through his many campaigns.
D) He proclaimed that he would not leave his kingdom to his bookish son.