The Atlantic has an interview with Sean McFate, who was a mercenary with DynCorp Intl., is faculty at the National Defense University, and author of a recent book, The Modern Mercenary: Private Armies and What They Mean for World Order.
A topic McFate manages to avoid, at least in the interview, is quasi-mercenary outfits like the French Foreign Legion, which are employed by a nationstate but are in fact soldiers for hire. A major role of our Green Berets is to recruit and train onsite proxy forces of indigenous troops or indigs to support U.S. aims.
For those interested in a fictional treatment of the subject of mercenaries, see the SF series concerning a future merc armor outfit called Hammer's Slammers, written by David Drake, mostly published by Baen Books. Or try Andre Norton's Star Guard, rereleased by Baen.
