"Why did the civilization die?"

Look at the title and you'll know what I spent my lesson doing. I focused on the decline of the Indus Valley Civilization, and discovered that there is hardly any evidence to support the theories that exist. There are four main ones: 1. Aryan invasion; 2. Changing course of rivers; 3. fall of the rulers; and 4. End of trade with Mesopotamia. In my opinion, it was the latter that seems most likely, although it could have been a combination of all of them! More info in the Internet, I hope!