Answer:
a) the death of the Emperor Charlemagne
Explanation:
Emperor Charlemagne or Charles the Great, was king of the Franks in 768-814 in which he later became the emperor of the West in 800-814. He founded the Holy Roman Empire, stimulated European economic and political life, etc.
After his death, his empire was invaded by Vikings which led to the local nobles to took over the duties of protecting their properties. This the did, through the raising of local armies. As this power passed to the local lords rather than the kings appointed by the emperor, it gave rise to feudalism.
