Question

How harappan civilization decline

Answer 1

They are many reasons for the decline of the harrapan civilization.. some the reasons were..
because of heavy floods caused by Indus river and it's tributaries.. another reason is because of the invasion of Aryans... from center Asia. and Hungary and Austria.. leads to decline of the harappan civilization...
another reason is because of the invasion of the Aryans these Indus people migrated to south Indian regions..

hope it helps you