Why did the Harappan civilization build the city of Mohenjo-Daro in the Indus Valley? Describe the city they built.

One theory suggested that a nomadic, Indo-European tribe called the Aryans invaded and conquered the Indus Valley Civilization, though more recent evidence tends to contradict this claim. Many scholars believe that the collapse of the Indus Valley Civilization was caused by climate change. Trade, writing, and seals all but disappeared from the area. Many believe that the decline of the Harappan civilization was a result of Aryan invasions from the north. This theory seems logical because the Aryans came to power in the Ganges Valley shortly after the Indus demise of the Indus Valley Civilization.