Perhaps the fierest debate on the Indus civilization is over the reasons for the end of the India’s earliest cities. Did they dramatically collapsed or was there steady urban decline? Was the decline a result of in roads by the Aryans or did rivers, earthquakes, or climatic shifts contribute to the disintegration? Was the end marked by a cultural fracture or regional migrations from the core areas to the areas which offered better subsistence possibilities? The recent studies do not accept the Aryan invasion theory or the inundation theory or the tectonic upliftment concept as it is not warranted by any scientific or rationale evidences. It seems likely that the decline of the Harappan civilization was mainly due to ecological imbalances. The delicate ecological balances of semi-arid areas (Harappa and Mohenjodaro) was being disturbed because the human and cattle populations in these areas was fast depleting the scanty forest, food and fuel resources. Thus, the growing populations of men and animals confronted by scanty resources wore out the landscape. This depletion of the subsistence base caused strain on the entire economy. Moreover, the drift of the monsoon to the west necessitated the Harappan people to migrate to the areas of Gujarat, Haryana which provided better survival possibilities.