What are the causes of Aryan migration?

Answer 1

A group of warrior nomads, the Aryans, began to migrate into the Indus Valley region around the time that the Harappan Civilization began to decline. Scholars disagree about whether the Aryans overtook the Harappan Civilization by force, or simply moved in and coexisted with them during their decline. Regardless, the nomadic Aryans were predominately a cattle-breeding society, and they learned how to live as settled agriculturists from the remaining Harappan people. Therefore, the Aryans absorbed remnants of the Harappan Civilization and integrated them into their own culture to form the Vedic culture. Since the Indus Valley Civilization left no written records, the nature of the transition from the Harappan culture to the resulting Vedic culture is that much more a mystery