Excellent Game of Thrones strikes me as excessively grim. I guess that was life like in the Middle Ages if you throw out theological debates, building of the great cathedrals, emerging science, engineering inventions and geographic discoveries: just power struggles between princes, murders and rape.
The society, invented by Martin has a social structure of Europe in the X Century but the resources and warmaking techniques of the XIV-XV Centuries. Thus, it all degenerates in unbelievable carnage. Naturally, the disordered societies of the Dark Ages had little resources to field large armies and fleets (probably, most "armies" numbered a few hundred men and a few dozen riders) and had little mobility because of the primitive logistics and poverty of the land. Population density was low and forests and rivers--impassable, so that, probably, many of the "conquered" tribes got aware that they were conquered only after several decades never having to meet their new overlords in flesh and blood. The warfare of the Late Middle Ages and Early Modern Europe was supported by denser populations but it was tampered by many strictures of the contemporary society: essentially extraterritorial nature of the Church, developing diplomacy, rise of the power of mercantile classes, etc. etc.
