Many experts believe that the decline of the ancient Aryan civilization was caused by environmental changes. Another theory suggests that a sharp rise in the Aryan population led to the decline.
One of the major factors that caused the decline of the Aryans was environmental changes. These changes included both increasing and decreasing amounts of rainfall. When there was more rainfall, massive flooding resulted, ruining irrigation systems and destroying buildings. The Aryan people damned the rivers, which increased flooding in some areas and shifted the river in others, keeping important flood waters from some cities and settlements. This water shortage caused a food shortage, making the cities vulnerable to outside attacks. People abandoned the cities to settle in more fertile areas.
These environmental changes also brought soil erosion, which was worsened because of deforestation. Much previously fertile land turned into deserts. The Aryans denuded forests so that they could use the trees for building materials. This also caused a loss of valuable natural resources.
The Aryan civilization thrived between 2500 and 1700 B.C. when nomad cattle herders migrated to the Indus River valley. The civilization started to decline around 1900 B.C. By 1700 B.C., most of the Aryan cities had been abandoned.