Indo-Aryan migration
Paleoclimatologists believe the fall of the Indus Valley Civilisation and eastward migration during the late Harappan period was due to climate change in the region, with a 200-year long drought being the major factor. The Indus Valley Civilisation seemed to slowly lose their urban cohesion, and their cities were gradually abandoned during the late Harappan period, followed by eastward migrations before the Indo-Aryan migration into the Indian subcontinent.