Most of the mature Harappan sites in the region of Cholistan had been abandoned during C. 1800 BCE. Simultaneously, there was an expansion of population into new settlements in Gujarat, Haryana and Western Uttar Pradesh.Several explanation for the decline of Harappan civilisation were climatic changes, deforestation, excessive floods, and the shifting/or drying up of rivers. The Harappan civilisation/Indus civilisation flourished around 2500 BC.