The correct answer to this open question is the following.
The historical circumstances that led to the establishment of settled societies in the Indus Valley were the following.
The Indus Valley civilization is one of the oldest cultures known on planet Earth.
Historians believe that the Indus civilization is as older as the Sumerians, in Mesopotamia.
Also known as the Harappan civilization, the first settlement of the Indus people was next to the Indus River. Since those ancestral times, the Harappans developed an important culture around agriculture. As a result of this, the Indus people strengthen their kingdom in the region. Because of this development, the Harappan people prospered and extended their territories.
But through the passing of years, they disappeared mysteriously due to factors unknown by historians and anthropologists. So after many years, other people that practiced Buddhism and Hinduism followed.