"...ethnicity is relative--if you grew up in a small, isolated community in northern England, those folks in southern England might as well have been in a different country as far as you were concerned. They'd speak with substantially different accents, perhaps be on the other side in a civil war, might practice their religion differently, etc. But at least they're still kinda English, unlike those Irish over there, who even in the 1800s were depicted by non-Irish as subhuman. Unusual hair or eye color for one's area could really stand out, for better or worse."
Now, Korea is obviously about as far from Europe as you can get, but the principles of human interaction, movement, culture, etc., are basically the same--that is, people have culture everywhere.
I read about the Paekchong of Korea over on Peter Frost's anthropology blog.
"Like Japan with its Burakumin, Korea used to have its own outcastes: the Paekchong (or Baekjeong)... As late as the mid-20th century, however, they still numbered over 50,000, with most living in segregated ghettoes."
"'Being an alien people from Tartar, the Yangsuchuk were hardly assimilated into the general population. Consequently, they wandered through the marshlands along the northwest coast. They were engaged in the making and selling of willow baskets. They were also proficient in slaughtering animals and had a liking for hunting. Selling their wives and daughters was part of their way of life.' (Rhim, 1974)"
"By the end of the 15th century, this attempt at integration was recognized as a failure...“they were left pretty much to their own devices, just so long as they did not disturb outsiders” (Passin, 1956). They were allowed to run their own communities and resolve internal disputes, except for serious crimes. They were also exempt from taxation, compulsory labor, and military service. Finally, they were given a monopoly over occupations that involved the taking of life (and which were considered ‘unclean’ by Buddhists), like butchery, leather making, dog catching, and capital punishment (Passin, 1956). These occupations often paid well..."
The article goes on, with some very interesting observations on the potential boringness of "normal" life and the culture of nomadic hunters, of relevance to anyone trying to get their head inside personality-culture interactions (personally, I think any good storyteller must have some understanding of the relationship between their characters' personalities and traits and the things their culture/s value (or denigrate). Our relationship with everyone else in society has a pretty big effect on our lives, after all. It is also a good idea for writers to remember that multiple cultures can (and generally do) exist within one society/nation/geographic territory, and the people in those groups often have complex and sometimes troubling relationships with each other.