Why did Sumerian city-state have a hard time creating empires?
The Sumer people were believed to have existed from 4500 ~ 2000 BC which includes the very famous Babylonian and Assyrian Empire. They were one of the tribes that were recorded to be the ancient Iraq. Later on, it has been divided into several city-states which are independent of each other.
The city-states that had been formed had their own system of governance: some built their own societies while others joined together and had mutual governance.