Matthew G. Marsh
Unlike the civilizations of Mesopotamia, Egypt, or China, the Indus Valley Civilization disappeared from history, leaving few traces of its existence. For reasons that are still unclear, between 1900 BCE—1700 BCE the Indus Valley Civilization went into decline, as its urban centers began to decay and were ultimately abandoned. The remaining outliers of the Indus Valley Civilization reverted to a pre-urban settlement type. The reasons cited by historians for its disappearance are numerous, often controversial, and, ultimately, inconclusive. What is clear is that by 1700 BCE the main cities of the Indus civilization (Harappa, Mohenjo-Daro, and Ganweriwala) were abandoned, and several smaller settlements saw severe depopulation. Alongside this sharp decline in urban population was a marked decrease in long-distance trade, a drop in the production of luxury items, and a general shift in population to the east.
There have been numerous theories as to the proximate cause of the decline of the Indus Civilization.
One of the earliest fully expounded theories was that of Mortimer Wheeler, who hypothesized that circa 1500 BCE, the Indo-Aryan tribes launched an armed invasion and destroyed the Indus Civilization. Due to his use of circumstantial evidence, and the fact that there is no evidence supporting the arrival of the Indo-Aryan tribes during the time of the Indus Civilization, Wheeler’s theory was discredited by the 1980s.
However, his theory still appears in some popular works on the Indus Civilization. Other explanations for the demise of the civilization include geological disruption of the Indus River, climatic change, and the loss of trade.
Regardless of the reason, by 1700 BCE the Indus Valley Civilization had vanished and, as the second millennium BCE drew to a close, a new people began slowly moving into the Indian subcontinent.[1]
[1]. Antonova et al., History of Ancient India, 27–29; Chopra et al., Comprehensive History, 21–22; Habib, The Indus Civilization, 62–66; Jha, Early India, 39–41; Mehta and Mehta, History of Ancient India, 110–15; Gregory L. Possehl, “The Transformation of the Indus Civilization,” Journal of World Prehistory 11, no. 4 (1997): 425–72; Sharma, India’s Ancient Past, 85–89; and R. E. M. Wheeler, “Sociological Aspects of the Harappa Civilization,” Ancient India 3 (1946): 74–78.