Not really a response to the thread as such, just an idea thrown out there: if you look at the areas that the Hellenic kingdoms and the Romans after them conquered and held in a reasonably stable, orderly fashion, they are largely areas that already had dense (by contemporary terms), cohesive, organized societies. The Romans could make 'good' provinces out of Gaul and southern Britain because the basic conditions for centralized control of the areas already existed: all the Romans had to do was co-opt the existing order. And even better example is Alexander's conquest of Achaemenid Persia: after only three major battles (and some sieges and so on), he inserted himself into the existing power structure, which he left largely unchanged, excepting that he was now in charge. The situation would have been much different had there not already been a highly organized central government for him to take over.

Does this mean that the converse is true, i.e., are the areas that Rome did not conquer bound to be ones without advanced societies? I don't want to group all non-Roman areas of the world under one rubric, but there might be a grain of truth to that idea.