Why did the Indus Valley Civilization decline?
The Indus Valley Civilization likely declined due to a combination of climate change reducing monsoon rainfall, the drying up or shifting of the Sarasvati/Ghaggar-Hakra River, disrupted trade networks, and possible tectonic activity. There is no evidence of a single violent conquest.
The decline of the Indus Valley Civilization around 1900 BCE remains one of history's most debated questions, partly because the Indus script remains undeciphered — we literally cannot read what the people themselves might have recorded about their troubles.
The most widely accepted explanation centers on climate change. Paleoclimate research has demonstrated a significant weakening of the Indian summer monsoon around 2000-1900 BCE, which would have reduced rainfall and river flow across the region. This would have been catastrophic for an agricultural civilization dependent on predictable water supplies.
Closely related is the theory that the Ghaggar-Hakra river system — which many scholars identify with the ancient Sarasvati mentioned in early Indian texts — changed course or dried up entirely. Many Indus Valley settlements were located along this river system, and its disappearance would have made continued habitation impossible.
Some researchers point to tectonic uplift that may have redirected rivers away from major cities. Others emphasize the disruption of the long-distance trade networks that connected the Indus Valley with Mesopotamia and Central Asia — potentially undermining the economic basis for urban life.
What seems clear is that the decline was gradual rather than sudden. Population shifted from large cities to smaller rural settlements, particularly in the east and south. Cultural traditions persisted in modified forms. The Indus civilization didn't so much collapse as it transformed — adapting to new environmental realities through de-urbanization and dispersal.