18. The collapse of empires typically begins with

political corruption and social inequity

Explanation:

As the corruption and inequity in the empire started to arise, the citizens tend to gradually built up resentment toward the ruling class. They blame them for having to live such luxurious live while letting the common people suffered and hungry.

In the end, they will started to gather together and formulate a way to overthrow their government. This is why revolutions occurs. They forcefully remove the nobles from their power and the empire would collapse.

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