I'm reading David Anthony's The Horse, The Wheel, and Language now, a book about the nomads who lived in the steppe north of the Black and Caspian seas between 4000 and 2500 BCE and spoke proto-Indo European. I stumbled across this book (actually, probably used Amazon's links to find it) after having read Patricia Crone's Slaves on Horses. This latter book, which is mainly about why Arab-Islamic societies so often were ruled by slave soldiers (Mamelukes, etc.). In her brief introduction, Crone makes fascinating comparisons between three initially nomadic, or at least non-state and often migratory, societies: the desert Arabs, the steppe Mongols, and the forest Germanic tribes. Her hypothesis, in a nutshell, is that the physical environment had significant effects on the respective social and political structures: in their very harsh environment the Arabs developed almost no structures beyond simple tribal egalitarianism (hence their unsuitability as rulers later on when they conquered developed civilizations and their need to rely on slave soldiers); the Mongols' wealth in horses and livestock actually allowed them to build up *some* patterns of rule, but not of a highly institutionalized nature; finally, the Germanic tribes lived in an underdeveloped (but ultimately developable) physical environment, where they were unmolested by outsiders (Mongols) and had the time to develop the stable structures that eventually became states.
Since these were just hints by Crone, albeit intriguing ones, I wanted to follow up on her book with something more up-to-date (Crone wrote around 1980) and more substantial. I should also say that these questions about the relationship of physical environment to culture/politics/etc interest me and may become the topic of a future project.
More updates on Anthony - and the proto-Indo Europeans - to follow.