Answer:
D The military was unable to defend the empire against neighboring powers.
Step-by-step explanation:
Cyru´s death happened on strange land, protecting the empire from a foreing invasion, he died on the modern day country of Kazakhstan, trying to attack an enemy tribe before they invaded the empire, as it was one of the largest empires ever seen it was hard to control and defend and this was the ruin for Cyru´s since he died trying to defend his land. After that