What are four seasons for the fall of the Indus Valley civilizations?

The collapse of the Indus Valley Civilizations can be attributed to the following factors. One, the trade networks declined and disappeared. This meant less work for traders and manufacturers. Two, changes in geography that caused the rivers to either dry up or change direction Three, the people abandoned the major cities. Four, without trade and access to water, people succumbed to disease and starvation.