Question

Which is a reason Sumer declined as a civilization? Sumerian city-states fought each other. Sumerian rulers outlawed religion. The climate changed drastically. The Tigris and Euphrates rivers dried up.

Answer 1

I believe the answer is: Sumerian rulers fought to gain territory

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Because of the conflict that happened between sumerian rulers, The territory of the Sumerian empire started to be divided/separated into smaller empires. This make it much more easier for opposing empire or barbarian to conquer them and pick them apart, which lead to the decline of Sumer civilizations.

Answer 2

"Sumerian city-states fought each other" would be the best option from the list, since this internal division led to a collapse of power that left people without protection or a solid economy.