Why did sumer most likely develop in mesopotamia?

Sumer most likely developed in Mesopotamia because they were the first to migrate to Mesopotamia, the snow melting provided a water source for the Sumerians, though the Mesopotamian climate isn't very good to flourish in they did create a civilization. The annual flooding from the melted snow deposited silt making the river banks good to plant crops at.
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Alexander Graham Bell invented the telephone.