The reasons for the eventual decline of the Indus Valley society are unclear. Competing theories contend (1) that it was destroyed by the incursion of [[Aryan]] peoples from central [[Asia]]; and (2) that the shifting of rivers had a catastrophic effect on the agricultural base. | The reasons for the eventual decline of the Indus Valley society are unclear. Competing theories contend (1) that it was destroyed by the incursion of [[Aryan]] peoples from central [[Asia]]; and (2) that the shifting of rivers had a catastrophic effect on the agricultural base. |