How did Mesopotamia, one of the most wonderful civilisations of the ancient world, decline is an interesting question to consider. It is said that the Sumerians ceased to exist as a civilisation by 2000 BC. Historians attribute many reasons for the fall of Mesopotamian Empire. Some say that there was overcrowding which subsequently led to pollution along with other reasons like war and changes in the environment. Mesopotamian cities also had major pollution problems.