What factors were responsible for the decline of the Harappan Civilisation?

Various factors were responsible for the decline of the Harappan Civilisation. Some of these are the followings

1. Natural Calamities like floods and earthquakes caused havoc and destroyed human habitation.
2. The invading Aryans destroyed Indus settlements.
3. Deforestation due to the excessive use of wood for making copper and bronze, to bake bricks, pottery, stone wear and to make boats and furniture, led to drying up of land and rendered it infertile.
4. Decrease in fertility because of increasing salinity of the soil caused by the expansion of the neighbouring desert.
5. Changes brought about in the course of the river Indus lead to the flooding of the hinterland of Mohenjo-daro and its ultimate decline.