I've read passing references to "Zomia," but had not known about the source of its current popularity until reading interesting review in the Chronicle of Higher Education: "The Battle Over Zomia," by Ruth Hammond. It discusses James C. Scott's book, The Art of Not Being Governed: An Anarchist History of Upland Southeast Asia (Yale University Press, 2009).
According to the article, his thesis is that the ethnic groups in the highlands of Southeast Asia are "barbarians by design, using their culture, farming practices, egalitarian political structures, prophet-led rebellions, and even their lack of writing systems to put distance between themselves and the states that wished to engulf them."
Since I haven't read the book, I can't comment in detail, but there are a few interesting points worth drawing out. (Also, the Hmong feature prominently in the book and two leaders in Hmong Studies comment in the review.)
One point that stands out is the discussion of ethnicity. Based on the review, it sounds like Scott is looking critically at ethnic identity in the context of politics. One critic in the piece suggests that this reduces the meaning of ethnicity for people within the group. The article continues:
Scott counters that what he has done in dissecting the hill peoples' identities "has been done for almost every other ethnic group, in terms of deconstructing their history and showing that ethnicity is a kind of positioning and a performance.
"It's usually a mistake," he says, "to imagine that there is a great deal of genetic and genealogical continuity."
His book, he insists, does nothing to diminish those groups' claims to autonomy, land rights, and recognition: "I think that every identity is historically constructed, and, in fact, you can argue that that is in a sense even more noble and worthy of recognition: the self-creation of an ethnic group."