Final answer:
The four causes of the downfall of the Indus Valley civilization were environmental degradation, climate change, disease, and invasions.
Step-by-step explanation:
The decline of the Indus Valley civilization is attributed to several factors:
- Environmental degradation: Years of resource exploitation and high population density led to environmental degradation, making the land unsuitable for human populations.
- Climate change: Changes in monsoon patterns and the shifting of the floodplain of the Indus River impacted the availability of water for drinking and irrigation, leading to population decline.
- Disease: Epidemic diseases could have further weakened the civilization, leaving them vulnerable to attacks.
- Invasions: Raiding groups like the Aryans could have taken advantage of the weakened state of the civilization and attacked.