A strong loyal army is neccesary to protect the empire from invaders.
This empires fell for the over conquering they had, they had not enough army to protect the whole empire, and in consequence whem invaders came, weren´t able to defend themselves.
The government should try to prevent internal rebelions
As the empires grew larger they invaded other cultures and people that weren´t their own, making changes to their cultures, this is one of the main reasons for rebelions within societies, the necessity of being govern by our own people.