Which main factor contributed to the downfall of Mesopotamia, Egypt, and the Kingdom of Kush?

A. bad agricultural practices

B. periods of drought

C. corruption and war

D. drastic population growth

Scientists believe that Mashkan-shapir's collapse was caused in part by destruction of the fields by mineral salts. When mineral salts concentrate in the upper levels of the soil, it becomes poisonous for plants. In Mesopotamia, irrigation was essential for crop production.