Around 1800 BC, signs of a gradual decline began to emerge, and by around
1700 BC, most of the cities were abandoned. However, the Indus Valley
Civilization did not disappear suddenly, and many elements of the Indus
Civilization can be found in later cultures. Current archaeological data
suggests that material culture classified as Late Harappan may have persisted
until at least c. 1000-900 BC, and was partially contemporaneous with the
Painted Grey Ware and perhaps early NBP cultures. Archaeologists have emphasised
that just as in most areas of the world, there was a continuous series of
cultural developments. These link "the so-called two major phases of
urbanisation in South Asia".
A possible natural reason for the IVC's decline is connected with climate change: The Indus valley climate grew significantly cooler and drier from about 1800 BC, linked to a general weaking of the monsoon at that time. Alternatively, a crucial factor may have been the disappearance of substantial portions of the Ghaggar Hakra river system. A tectonic event may have diverted the system's sources toward the Ganges Plain, though there is some uncertainty about the date of this event. Although this particular factor is speculative, and not generally accepted, the decline of the IVC, as with any other civilization, will have been due to a combination of various reasons. New geological research is now being conducted by a group lead by Peter Clift, from University of Aberdeen to investiagte how the courses of rivers have changed in this region since 8000 years ago in order to test whether climate or river reorganizations are responsible for the decline of the Harappan.
In the course of the 2nd millennium BC, remnants of the IVC's culture (the so-called Cemetery H culture) would amalgamate with those of Indo-Aryan peoples according to Indo Aryan Invasion or Migration theory, likely contributing to what eventually resulted in the rise of Vedic culture and eventually historical Hinduism. Judging from the abundant figurines, which may depict female fertility, that they left behind, some assume that IVC people worshipped a Mother goddess (compare Shakti and Kali, several thousands years later). However, there is no firm agreement among experts as to whether or not these figurines actually depict female fertility, or if they depict something else. Also these people ate beef and buried their dead. IVC seals depict animals, perhaps as the objects of veneration, comparable to the zoomorphic aspects of some Hindu gods. Seals that some think resemble Pashupati in a yogic posture have also been discovered.
In the aftermath of the Indus Civilization's collapse, regional cultures emerged, to varying degrees showing the influence of the Indus Civilization. In the formerly great city of Harappa, burials have been found that correspond to a regional culture called the Cemetery H culture. At the same time, the Ochre Coloured Pottery culture expanded from Rajasthan into the Gangetic Plain. The Cemetery H culture has the earliest evidence for cremation, a practice dominant in Hinduism until today.