Who took control of india after the disappearance of the indus valley civilization in 1750 bce? how do we know about them?

The Indus Valley Civilization started to decline around 1800 BCE because of the climate change and migration. There is a theory that claims that a nomadic, Indo-European tribe, known as the Aryans, attacked and dominated the Indus Valley Civilization. With these, the small community could not produce the agricultural superfluities necessary to sustain cities, which were then abandoned.