Final answer:
The decline of the Monsoon Marketplace can be attributed to factors such as changes in the floodplain of the Indus River and the monsoon pattern of wind and rainfall. Environmental degradation and population growth may have also contributed to the decline. The exact cause of the decline remains uncertain.
Step-by-step explanation:
The decline of the Monsoon Marketplace can be traced back to the shift in the floodplain of the Indus River around 2000 BCE, which created dry river beds and led to a lack of water for drinking and irrigation. Changes in the monsoon pattern of wind and rainfall in South Asia could have been responsible for these environmental effects. Another theory suggests that environmental degradation caused by urbanization and population growth also played a role in the decline. The decline occurred over a period of several centuries and the exact cause remains uncertain.