Why did this Indus Valley civilization end? Some of the older theories was maybe it was a foreign invasion, maybe some of the ancestors of the modern Indians invaded, and maybe they assimilated it somehow. More current theories don't think that was the case. They think it might be some form of climate change that some of the important rivers dried up, made the agriculture much harder. Some people think it might have been a natural disaster, it might have been a flood of some kind, but we just don't know. Or the people, for some reason, decided to leave, die, migrate to maybe other parts of the region. But needless to say, it was a significant civilization, and we're just scratching the surface of what we know about it.