What evidences have been put forward to explain the collapse of the Harappan Civilization?

The Harappan civilisation was one of the earliest and the most advanced civilisation in the world. The civilisation was spread in the cities of the Sind in Pakistan and Gujarat, Rajasthan, Haryana and Punjab in India. The civilisation flourished in the area with the development of many cites like the Harappa, Mohenjo-Daro, Lothal, Cholistan and many others. But evidence suggests that by 1800 BCE most of the Mature Harappan sites in the near Cholistan and other regions have been abandoned. Consequentially, the population into new settlements in Gujarat, Haryana and western Uttar Pradesh expanded.

In the Harappan sites that continued to be occupied after 1900, all the distinguishing artefacts including weights, seals and special beads were found lost. Writing, trade, and specialisation also disappeared. House construction techniques declined and no large public structures were made. All these developments indicated the beginning of the Late Harappan age or successor cultures.

Many historians and experts attribute this to natural causes and calamities like climate change, deforestation, floods, shifting and drying up of rivers and the overuse of landscape. But these causes do not explain the downfall of the civilisation as a whole. A strong combining element was responsible for the downfall of the civilisation as a whole.