Mercenary
A mercenary is a person who takes part in an armed conflict who is not a national of a Party to the conflict and "is motivated to take part in the hostilities essentially by the desire for private gain and, in fact, is promised, by or on behalf of a Party to the conflict, material compensation substantially in excess of that promised or paid to combatants of similar ranks and functions in the armed forces of that Party".
http://en.wikipedia.org/wiki/Mercinary#Mercenaries_through_history
------------------------------------------
Private Military Companies (PMCs)
A strand of the contemporary mercenary trade sometimes goes under the label of the Private military company or PMC, which provides logistics, manpower, training and other services. PMCs' contractors are civilians (in governments, international and non-governmental organizations) authorized to accompany a force in the field. Hence, the terminology "civilian contractor" is sometimes used. PMCs may use force, hence they can be defined as: "legally established enterprises that make a profit by either providing services involving the potential exercise of force in a systematic way and by military means, and/or by the transfer of that potential to clients through training and other practices, such as logistics support, equipment procurement, and intelligence gathering".[12]
-------------------------------------
In 2004 the industry was given a huge boost because PMCs were employed by the US and other coalition members to do security work in Iraq. In March 2004, four employees of Blackwater USA who were guarding food shipments were attacked and killed in Fallujah. In the well publicised incident, the killings and subsequent desecration of the bodies were contributory causes for the First Battle of Fallujah, which occurred shortly after the killings. PMCs also received a boost from Afghanistan operations, where many PMC employees serve as private security forces for heads of state such as Hamid Karzai.[citation needed]