From opportunistic guns for hire on the fringe of domestic conflicts to a global force operating within a multi-billion dollar industry. The world of the military mercenary has become big business.
Private companies have taken on an increasing range of responsibilities as war is outsourced, from security and intelligence analysis, to training and combat roles.
It has been a controversial issue, and the US State Department has offered assurances that it has strengthened rules governing private security firms in the wake of a 2007 shooting in Iraq in which 14 civilians were killed.
A court in Washington, DC on Monday sentenced a former Blackwater guard to life in prison and three others to 30 years each for their role in the mass shooting in Baghdad.
The prosecutor described it as an "unprovoked ambush of civilians".
The incident cast a spotlight on the use of private contractors in conflict zones, and raised questions about oversight and accountability.
Have soldiers of fortune become an inevitable part of modern conflict? Or does the use of private contractors risk undermining the law of war?
Presenter: Shiulie Ghosh
Sean McFate, a former military contractor and author of the book The Modern Mercenary.
Molly Dunigan, a political scientist who researches private military contractors at the RAND Corporation.
Phyllis Bennis, a fellow at the Institute for Policy Studies, and author of Understanding ISIS and the New Global War on Terror.
Source: Al Jazeera