This is an excerpt from a research paper in which Colonel Dodenhoff quite exhaustively examines the problem of employing mercenaries, using the Congo as a case study.
Dodenhoff, George H.
"A Historical Perspective of Mercenaries,"
Naval War College Review: Vol. 22
, Article 9.
Available at: http://digital-commons.usnwc.edu/nwc-review/vol22/iss3/9