Reason points out a fascinating lecture [podcast only] by James C. Scott, South East Asian scholar and political historian.

Scott argues that South East Asian hill tribes should be seen as an evolved culture of statelessness, not a archaeological relic from before the existence of the state.

The lecture is a preview of a forthcoming book. He uses hills and valleys as the main divisor of historical "statefulness" in SE Asia. Keeping in mind that for most of its history, most states have had a tyrannical relationship with their subjects, he casts those outside or at the periphery of a state as there by choice, more like political, religious or economic refugees than barbarians. He also emphasises that the flow of population into and out of states has been very much two-way depending on the relative prosperity and coherence of a kingdom within larger cycles of dynastic formation and collapse.

To support this, he points out, amongst other things, that forms of valley agriculture such as wet rice farming are particularly easy for a state to control - monocropped, relatively immobile capital investment in oxen and tilled land, seasonal and therefore prone to extortion in that season, and so on. Another point that stuck out was that almost every hill tribe has an origin myth where they had writing, but lost it. They lost it either through accident, such as their writing was on a cake which they had to eat, or through malice, such as someone stealing or destroying it.

There's no transcript so I can't readily quote to give it justice. This is not the only reframing of the relationship between successful empires and their barbarian (or otherwise) neighbours about, but it states the case more boldly and clearly than I've seen before.