1491, by Charles C. Mann

I really liked it. It is really interesting to think of what would have happened in the new world, if the old world had never come along. 2000 years later, would they have looked back on the poets and philosophers that existed at the time the way we look back on early greeks? We only have a sample of the types of thoughts they were thinking - almost all of it was burned up and destroyed before anything could be understood. So it's likely that their best thinkers who were around in 1400 have left nothing behind today.