What happened when the Indian Aryans invaded the South Asian subcontinent in the 4th century BC/KLOC-0?

The Aryans' original hometown was the grassland in southern Russia, and later they migrated from this area to Asia and Europe. Among them, an Indian Iranian, after a period of wandering, settled in the plains of the two river basins in Central Asia (Amu Darya and Syr Darya). About14th century BC, one of the Indian Iranians entered the South Asian subcontinent and was called the Indian Aryan (only Aryan was found in ancient Indian literature). The other one entered Iran and was called Iranian Aryan.

Aryans in India first settled in the Seven Rivers (or Five Rivers) in the upper reaches of the Indus River. At that time, animal husbandry was dominant, and agriculture was only a part-time job. Urban civilization has not yet appeared. Most of Rigveda's hymns were compiled in this area. The upper limit of compilation time is about 1200 BC, or earlier. After they invaded the Qihe River basin, they conquered the local aborigines and lived in the era of military democracy at the end of primitive society. Later, they developed into the Ganges River basin in the east, and then extended to parts of South India. After they entered these areas, primitive tribal organizations gradually disintegrated and tribal alliances appeared. There are constant wars between alliances. At the beginning of 1000 BC, with the appearance of ironware, a few advanced tribes in Aryan, India began to transition to the country. By the 6th century BC, more than 20 small countries had formed in Ganges River Basin, Indus River Basin and parts of South India, and entered the "Sixteen Countries" era in the history of Indian subcontinent, or the national era. In the process of Indian Aryans expanding to the southeast, local residents were either conquered or dispersed and became the main residents of the ancient Indian subcontinent. At that time, the Varna system had just appeared, religion was still in its infancy, and it was worshipped by many gods.