Explanation – Many historians and archaeologists believe that a combination of factors, including changes in climate, environmental degradation, and resource depletion, contributed to the decline of the Indus Valley Civilization. There is evidence of shifts in river courses, reduced rainfall, and ecological stress that could have adversely affected the sustainability of the civilization. Dark Age is the time frame from the decline of the Indus Valley Civilization around 4,000 years ago (early 2nd millennium BCE) until the rise of the Iron Age and Mahajanapada cities like Gandhar, Koshal, and Avanti (6th-5th century BCE).

Source: Forum IAS