This past month I've been fascinated by The Horse, the Wheel and Language by David Anthony. Anthony takes linguists' work on Proto-Indo-European (the mother of modern languages as varied as Sanskrit, Latin, Greek and English) and links it to archaeological studies, including his own, to theorize where Proto-Indo-European was spoken and how it spread. Although I tend to skim the many chapters of archaeological evidence, there is some really interesting stuff in here, like the Proto-Indo-European creation myth.
Anthony offers compelling evidence for the theory that horse-riding herders from the steppes around the Black Sea, wanting more pasture land in order to maximize their wealth, spread westward towards modern-day Hungary and beyond (and finally eastward toward India). He argues that the language spread not due to strictly military invasions, but due to a system resembling modern day franchises, where chiefs offered protection to native farmers in return for the best land for their herds. Natives began to speak the more prestigious Indo-European dialect. If you lived within this system, you followed a strict code of hospitality. The English words "guest" and "host" both come from the same Proto-Indo-European root, which has been reconstructed as *ghost-ti.