Answer:
No ruler was powerful enough to take over the other city-states.
Step-by-step explanation:
The major factor that prevented the Mesopotamian city-states from uniting with each other before 2400 BCE was the lack of powerful king. After the coming of powerful king Sargon the Great, these city states were united and make a great empire. Sargon the Great was the founder and first ruler of Akkadian Empire. He was also assumed as the first person who ruled over a big vast empire.