The Indus Valley Civilization flourished during the period of 2500-1900 BC in the basins of the Indus River wherefore it derives its name. The civilization's downfall is believed to have been caused by climate change, specifically a shift to a more arid climate. This would have led to a decrease in agricultural productivity, making it difficult for the people of the civilization to sustain themselves.
2. Overpopulation
The Indus Valley Civilization was one of the largest urban civilizations of its time, with a population of around 5 million people. This put a strain on the environment and resources, and may have led to deforestation, soil erosion, and other problems.
3. Deforestation
The Indus Valley Civilization was located in a region with a fragile ecosystem. The people of the civilization used wood for building, cooking, and other purposes, which led to deforestation. This would have had a negative impact on the environment and contributed to the decline of the civilization.
4. Invasion
The Indus Valley Civilization was also vulnerable to invasion from outside forces. Around 1500 BC, a group of nomadic people from Central Asia called the Aryans invaded the region and conquered the Indus Valley Civilization. The Aryans brought with them a new culture and religion, and their conquest marked the end of the Indus Valley Civilization.
5. Combination of factors
It is likely that the Indus Valley Civilization declined due to a combination of factors, including climate change, overpopulation, deforestation, and invasion. The exact cause of the civilization's downfall is still debated, but these are some of the most likely factors.