The End of Indus Valley Civilization
There is no general agreement regarding the causes of the breakdown of Harappan urban society. Some theories of ending of the Indus Valley Civilization is mentioned below-
1. The first is gradual environmental change, such as a shift in climatic patterns and consequent agricultural disaster, perhaps resulting from excessive environmental stress caused by population growth and overexploitation of resources.
2. Secondly, some scholars have postulated more-precipitous environmental changes, such as tectonic events leading to the flooding of Mohenjo-daro, the drying up of the Sarawati River, or other such calamities.
3. Thirdly, it is conceivable that human activities, such as invasions of tribespeople from the hills to the west of the Indus valley, perhaps even Indo-Aryans, contributed to the breakdown of Indus external trade links or more directly disrupted the cities.
4. The fourth theory posits the occurrence of an epidemic or a similar agent of devastation. It appears likely that some complex of natural forces compromised the fabric of society and that subsequent human intervention hastened its complete breakdown.