[SunkenCiv]

There was climate change involved, but the Indus Valley civilization was overrun; the Aryan invasion is denied today of course, for political reasons, but they came from Central Asia, and left due to some kind of climate change. Similar, later movements from Central Asia, but into Europe, are well known.

[CarrotAndStick]

Thanks! The Indus settlements are one of the big enigmas of mankind.