This (http://www.thenational.ae/apps/pbcs.dll/article?AID=/20100408/REVIEW/704089990)is a grim article about the Lord's Resistance Army operating in and around Uganda.
It's not pleasant reading, but if you can stomach the rape and torture it provides an interesting insight into how small nomadic groups can survive in territories nominally controlled by larger and more powerful military forces.
It's relevant to RPGs because wandering tribes feature in many game settings, whether they're barbarians, orcs or radioactive mutants.