Why does the region of the Indus Valley civilization de-urbanize after Vedic culture becomes dominant. No where does there seem to evidence of an invasion, and even if there was one the people of the Vedic culture don't refer to themselves as non native Indians ( as the Turks did in later invasions ), Where do things like Urban planning, Trade based economy, sophisticated drainage system go. Some people suggest a migration to the south, but how can a region lose all of these things and have virtually no remnants(there don't seem to any in South India)?
At the same time the Vedic culture seems to be outclassing everybody in language, law, philosophy, mythology etc.
Why does one culture despite being completely urban not able to develop sophisticated language philosophy, and even proper manuscripts, on the other hand one is able to do all of that despite being rural and agrarian?
This leads me to another question - what kind of an economy seems to be sustainable in a pre industrial age - an agrarian/trade based one or a war economy?
One theory is that the Vedic civilization started using wood instead of mud bricks or stones. And wood gets decomposed easily hence we don't see many artefacts.
If you look at the 2 periods culturally, there's not much gap. It feels like a natural period of continuation.
Another reason could be infighting due to rise of new states.