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PRIVATE MILITARY CONTRACTORS, PARAMILITARIES AND MERCENARIES …
3. Acts of Aggression
If it is found that another State, such as the United States or Russia, has directed
or influenced PMSCs, paramilitaries, or mercenaries on Ukrainian soil, such action
could amount to an instance of aggression. Furthermore, if such an act did occur, and
it goes unchecked according to international law, it could set a dangerous precedent.
The concept of aggression may be found in customary international law,40 but this
is not to say this statement means that the crime of aggression is unquestionably
reflected in customary international law. Whether a crime is considered to be a violation
of customary international law is often debatable and depends on two factors: actions
of States and opinio juris, both of which are in a continuous State of development.
Although many States do not regularly engage in acts of aggression, there are
certainly very significant exceptions. The current situation in Ukraine may prove to
be an even more significant exception. Even so, State practice against committing
aggressive acts is not conclusive. Until recently, it can be argued that there was not an
internationally agreed upon definition for the crime of aggression.41 Therefore, there
has been no opinio juris on what actually constitutes prohibited acts of aggression.
Even the alleged ‘consensus definition’ of the 1974 General Assembly Resolution
3314 (which will be explained infra), was “laced with ambiguous clauses to enable
parties to interpret it to suit their own political advantage.”42
On the other hand, however, there are well-respected scholars, such as Cherif
Bassiouni, who maintain that “aggression is a customary international crime that
requires no further definition or is subject to universal jurisdiction as a peremptory
norm from which there can be no derogation.”43 Furthermore, in the United
Kingdom, British Law Lord Bingham of Cornhill stated in a 2006 case, ‘“the core
elements of the crime of aggression have been understood, at least since 1945, with
sufficient clarity to permit the lawful trial (and, on conviction, punishment) of those
accused of this most serious crime. It is unhistorical to suppose that the elements of the
crime were clear in 1945 but have since become in any way obscure.’”44 Considering this
significant controversy over an agreed-upon definition and legal standing of aggression,
the following section will cursorily explore the legal development aggression has taken
over the past century with an aim to develop whether it is present in Ukraine, and
if so, what this means for the crime’s development under international law. In other
words, while the world is waiting to see if the International Criminal Court will finally
40 Jordan J. Paust, et al. , International Criminal Law, Cases and Materials, 3rd ed. (2001), p. 547.
41 Amendments to Article 8 of the Rome Statute, Resolution RC/Res.6, The Crime of Aggression, 11 June
2010, Annex I. Article 2(1) of the Kampala Amendment defines aggression as the “planning, preparation,
initiation or execution, by a person in a position effectively to exercise control over or to direct the
political or military action of a State, of an act of aggression which, by its character, gravity and scale,
constitutes a manifest violation of the Charter of the United Nations.”
42 Benjamin B. Ferencz, Reconciling Legitimate Concerns and Removing the Lock From the Courthouse Door
(2008), available at
43 Ibid.
44 Ibid.