Jared Diamond's book makes a great deal of sense to me in terms of the last 5,000 years. Agriculturalists moved in with domesticated animals throughout a great deal of Western Europe decimating prior populations with disease. The Celtic Warrior saga is a bit to dramatic for me. Disease makes a lot more sense as it did in the Americas. Violence happened, but disease decimated the aboriginal population in the Americas and Europe more potently.
http://en.wikipedia.org/wiki/Guns,_Germs,_and_Steel