The anti-mercenary norm and the market for combat force

Date01 March 2021
AuthorUlrich Petersohn
Publication Date01 March 2021
SubjectScholarly Essay
Scholarly Essay
International Journal
The anti-mercenary
2021, Vol. 76(1) 106–128
! The Author(s) 2021
norm and the market
Article reuse guidelines:
for combat force
DOI: 10.1177/0020702021994519
Ulrich Petersohn
University of Liverpool
Since 2013, combat services have been increasingly exchanged on the market. This
development is puzzling since the practice emerged despite an anti-mercenary norm
banning such services, and without any revision of the norm. The article argues that the
combat market is not a deliberate design, but the result of strategic interaction. For
some, compliance with the anti-mercenary norm is the best strategy, while for others,
violating the norm is best. However, once the norm violation occurs, it is in the interest
of all actors to maintain a fac¸ade of compliance. Non-compliant actors benefit from the
combat services, and compliant actors do not have to engage in costly sanctioning of
the norm violation, and avoid the reputational costs associated with non-enforcement.
The article employs game theory to investigate the strategic interactions of actors
across eleven combat contracts from 2013 to 2019.
Private military and security company, game theory, anti-mercenary norm, market for
force, international norms
In February 2018, operators of a Russian private military and security company
(PMSC) attacked a US military outpost in Syria. The event was a strong indication
of a significant development: combat services are frequently and regularly
Corresponding author:
Ulrich Petersohn, Department of Politics, University of Liverpool, Roxby Building, Liverpool, L69 7ZR, UK.

exchanged on the market.1 The exchange of combat services is surprising as it runs
counter to an established norm—the anti-mercenary norm. The norm reflects a
longstanding aversion—going back at least to the beginning of the nineteenth
century—of international society to private force providers.2
Violations of the norm are not a new phenomenon. In the 1960s and 1970s,
when groups of mercenaries were participating in civil wars in Congo and Angola,
an extensive international debate developed. As a result, the UN General
Assembly and the UN Security Council issued several resolutions condemning
the practice, describing mercenaries as dangerous criminals. At the same time,
Convention against Recruitment, Use, Financing and Training of Mercenaries
and the Organization of African Unity Convention on Mercenaries.3 Later, in
the mid-1990s—when the market for force experienced a quantum leap, turning
into a corporate market, and PMSCs provided combat services on a highly pro-
fessional level—international and national actors criticized the practice immedi-
ately.4 Some considered corporate actors to be different from mercenaries, while
others deemed them to be the “new mercenaries.”5 However, it was neither the
corporate structure nor the legal contractual relations that provided the differen-
tiation between illegitimate mercenary and legitimate activity. Rather, the type of
service differentiated one from the other. Any actor, be it an individual, group, or
corporation was considered to be a mercenary if they provided offensive combat
services. PMSCs therefore did “not entirely escape the anti-mercenary norm” if
they offered such services.6 However, as long as they provided defensive services
only, even in a conflict zone, their activities were considered to be appropriate and
not in violation of the anti-mercenary norm.
This differentiation has been reflected in the 2008 Montreux Document.7 With
fifty-four members to date, the agreement enjoys wide support within the interna-
tional community, including major international actors that are home to the larg-
est PMSC markets (e.g., the US, the UK, Canada, France, South Africa, and
Mark Galeotti, “Moscow’s mercenaries in Syria,” War on the Rocks, 5 April 2016, https://waronth
(accessed 5 November 2019).
Janice Thomson, Mercenaries, Pirates, and Sovereigns (Princeton: Princeton University Press,
Sarah V. Percy, “Mercenaries: Strong norm, weak law,” International Organization, 61, no. 4 (2007):
367–397, 373–374.
UK Government, Foreign and Commonwealth Office, Private Military Companies: Options for
Regulation (London: UK Government, 2002); UK Government, Foreign Affairs Committee,
Memorandum from Armor Group Services Limited, Appendix 6 (London: UK Government,
2002); and US Government, Committee on Oversight and Government Reform, Hearing on
Blackwater USA (2 October) (Washington, DC: US Government, 2007).
Peter Singer, Corporate Warriors (Ithaca: Cornell University Press, 2003); and Juan Zarate, “The
emergence of a new dog of war: Private security companies, international law and the new world
disorder,” Stanford Journal of International Law 34, no. 1 (1998): 75–165.
Sarah Percy, Mercenaries: The History of a Norm in International Relations (Oxford; New York:
Oxford University Press, 2007), 242.
Ulrich Petersohn, “Reframing the anti-mercenary norm: Private military and security companies
and mercenarism,” International Journal 69, no. 4 (2014): 475–493.

International Journal 76(1)
Germany) as well as states that have been significantly affected by armed security
providers (e.g., Sierra Leone, Iraq, Afghanistan, and Angola). Accordingly, while
security providers remained in business, combat providers disappeared again.8
However, the most recent re-emergence of combat contractors, in contrast to pre-
vious increases in mercenary activity, did not cause any debate or reshaping of the
anti-mercenary norm. The article thus investigates the following question: why is
there an active market for combat services, despite the presence of an anti-mercenary
The article will argue that the combat market is an institution that did not
emerge through a deliberate process but rather as an unintended consequence of
strategic interactions among states. The investigation will proceed in two steps. In
the first step, the existence of a combat market will be demonstrated. The claim
that there is regular and frequent exchange of combat services requires corrobo-
ration. In the second step, the exchange of combat services on a market, despite the
presence of an anti-mercenary norm, will be explained. As will be demonstrated,
the most likely theoretical explanations—a transnational coalition of actors cam-
paigning for the exchange of combat services, or a broad international discourse
on the legitimacy of private combat services—fail to account for the re-emergence
of combat providers.9
To clarify and further substantiate the argument, the article will draw on game
theory. From a game theoretic perspective, an institution is considered to be a self-
enforcing pattern of behaviour (equilibrium). As such, the combat market emerges
as stable through several sequential games. In the first—the norm compliance
game—market actors decide whether to comply with or defect from the anti-
mercenary norm (i.e., whether to trade defensive or offensive services). Because
the benefits of compliance and non-compliance are distributed unevenly on the
market, an equilibrium emerges with a larger group complying and a smaller group
defecting. However, it is not until the next subgame that the equilibrium becomes
stable. In the norm enforcement game, compliant actors have the ability to
increase the cost of defection through punishment. However, punishment is
costly for punishers as well; hence compliant actors would prefer to avoid enforcing
the anti-mercenary norm. Although tempting, this strategy can turn out to be costly,
as non-enforcement may be observed and sanctioned by an international audience.
Once the norm violation has occurred, compliant and defecting actors have a similar
interest: to avoid drawing the attention of their audience. Accordingly, both actors
tacitly collude and take actions to maintain a compliance fac¸ade.10 As a conse-
quence, the combat market emerges as a stable self-enforcing equilibrium.
8. Percy, Mercenaries, 227.
9. Martha Finnemore and Kathryn Sikkink, “International norm dynamics and political change,”
International Organization 52, no. 4 (1998): 887–917; and Elke Krahmann, “From ‘mercenaries’ to
‘private security contractors’: The (re)construction of armed security providers in international legal
discourses,” Millennium– Journal of International Studies 40, no. 2 (2012): 343–363.
10. Austin Carson, “Facing off and saving face: Covert intervention and escalation management in the
Korean War,” International Organization 70, no. 1 (2015): 103–131, 105.

In order to test the validity of this theoretical argument, the congruence method
will be employed. This method emphasizes consistency between precise theoretical
predictions and actual observable outcomes.11 This method lends itself to testing
game theory arguments because the underlying calculations of actors cannot be
directly observed, but the associated behaviour can. The more consistent the predicted
and observed patterns are, the higher the likelihood of the theory being valid.
A market for force
The article puts forward the claim that a combat market has been established since
2013. In general, a market institution is a stable and persistent pattern of behaviour
(self-enforcing equilibrium) organized around social factors such as...

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