The Indo- Aryans migrated from Central Asia and Persia to the subcontinent of India between 1800 BCE and 1500 BCE. Aryans started settling into most parts of Indus Valley and Ganges Plain since then.
Though at the early stage, migration was taken as an act of invasion, the Aryans came into for the sole purpose of settling in the Indus Valley Civilization. They used Indo-European language to communicate.
They started farming and looking after the farm animals as per their primary occupation, just like the other Indus Valley citizen. With the time people of Indus Valley accepted the presence of the migrated Aryans and worked together for the advancement of the valley towards the urbanization.
