Explain two theories as to why the ancient cities of the Indus Valley vanished.

It is somewhat of a mystery what caused the decline of the great cities of Harappa and Mohenjo-Daro on the Indus River. In the past, it was thought that the arrival of the Aryans to the region caused the decline. Archaeological evidence has refuted this claim. The archaeological data suggests the decline occurred hundreds of years before the Aryans migrated to the river valley.

While the decline of the cities is still not entirely clear,...

It is somewhat of a mystery what caused the decline of the great cities of Harappa and Mohenjo-Daro on the Indus River. In the past, it was thought that the arrival of the Aryans to the region caused the decline. Archaeological evidence has refuted this claim. The archaeological data suggests the decline occurred hundreds of years before the Aryans migrated to the river valley.

While the decline of the cities is still not entirely clear, one theory suggests a tributary of the Indus River, the Saraswati, dried up, which affected the vital farming industry. It is likely that floods also occurred as a result. Flooding was a common concern in the river valley as the Indus River was very unpredictable. To continually have to rebuild these advanced urban areas would have taken an immense toll on the resources of the civilization. The floods would also have disrupted farming. The reduced food surpluses affected trade and food supply, leading to famine and disease.

Another theory suggests that the collapse of the cities was caused by climate change. The climate change theory suggests the monsoons migrated eastward. This shift would have reduced the water supply, which had the same effect on farming as the previous scenario.