Final answer:
The Harappan civilization may have declined due to environmental degradation, migrations, invasions, and economic challenges.
Step-by-step explanation:
The decline of the Harappan civilization is believed to have been caused by a combination of factors. One possible reason is environmental degradation, such as the drying up of the river system that the civilization relied on for irrigation and agriculture. Another factor could be the influx of migrating populations and invasions from other regions, which could have disrupted the stability of the civilization. Additionally, economic challenges and shifts in trade patterns might have contributed to the decline.
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