Answer by Balaji Viswanathan:
What happened to the Indus Valley Civilization? This is one the least understood ancient civilizations and the largest of the bronze age cultures.
- We don't know the extent of the civilization. Just this year, the biggest Harappan site was found 2 hours from Delhi. Previously the civilization was assumed to be in the western corner of India, along Indus. If the largest site is close to the heart of India, maybe it extended as far as the Ganges plains?That would fundamentally rewrite the history of South Asia. We don't know.
- Deciphering the language. For a civilization with so advanced architecture and town planning, there must have been an advanced communication mechanism. We know little about the language they used.
- How they really ended. For a civilization that had a quarter of the world population at its peak, the culture had ended in a poof. Drought is the most cited cause. We have little clue of how the people moved on from the cities they so painstakingly built. There is such a dark hole in Indian history from about 1500-500 BC that it is so disconcerting. To add salt in the wounds, India's epics talk of some extraordinary things that happened in this period, but they have no historical or aracheological background.
- Was the mythical Bharata related to IVC: India's native name is Bharat – named after the "mythical" king. Vedas say that this guy belonged to the tribethat lived along the banks of Saravasti – a tributary of Indus. The time period that Vedas mention somewhat aligns with last stage of the IVC. After 25 generations from Bharata, Mahabharata is said to have happened [approx 500 years] and the Mahabharata itself happened a few centuries before the Nandas. That puts Bharata in the IVC period. These are all hypothesis and historians don't have anything to go further on this line. This huge disconnected path is a big unknown in Indian history.