By 1800 BCE, the Indus Valley civilization was in decline.•Although earlier scholars had supposed that this decline was brought about by attacks from invading Aryans, it has more recently been suggested that thecivilization may have declined from internal reasons, and that the people of the region moved eastwards in the direction of the Gangetic plain.•In addition to the immigration of new people from elsewhere, climate change, floods, and deforestation could have undermined the stability of the urban centers, leading to political decentralization