Irrigation of crops led to salinization of the soil, Sumer was located on a flat plain that provided no natural barriers to invasion, and the land became too swampy to grow adequate crops.
One geographic factor leading to decline of Sumer is their land itself. The people were poisoning their own land at the time, but they didn't that their water was causing this. Just as we do not drink salt water, plants aren't supposed to get salt water. The Sumerians at this time were starting fights with each other and they would go against their own civilization trying to prove who was the strongest. Unfortunatley, the Akkadian's had an idea that these people were easy prey, bringing them down one by one.
