How did the sumerians city-state lose power?

Answer 1

In their warfare between each other to acquite and protect their land an water, some cities became dominant and established control over lesser cities, establishing first concederations, then empires, the first of which was Akkad uner Sargon, who established an empire in the later 3rd Millennium BCEcovering Mesopotamia, the Levant and part of today's Iran. The cities lost independence under this rule.