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International law prohibits the use of mercenaries in armed conflict and certain peaceful situations.

Owing to its special nature, the law of armed conflict (international humanitarian law) does not address the legality of mercenary activities or establish the responsibility for mercenarism of those who participate in mercenary activities. Instead, it defines the status of a mercenary and its implications in the event of capture.

International standards

Hague Convention V respecting the Rights and Duties of Neutral Powers and Persons in Case of War on Land (1907), article

Article 4 of the Hague Convention V (considered to represent customary law) stipulates that �[c]orps of combatants cannot be formed nor recruiting agencies opened on the territory of a neutral Power to assist the belligerents�. The neutral Power thus has an obligation to prevent such activities from occurring on its territory. However, it cannot be held responsible where individuals cross the border of their own accord to offer their services to the belligerents. This article in effect creates an obligation for States to prevent the formation of mercenary groups on their territory for the purpose of intervention in an armed conflict to which they have chosen to remain neutral. If they fail to do so, they are in violation of their obligations under international law.

Charter of the United Nations (1945), article 2, paragraph 4

Article 2, paragraph 4 of the UN Charter stipulates that: "All Members shall refrain in their international relations from the threat or use of force against the territorial integrity or political independence of any state, or in any other manner inconsistent with the Purposes of the United Nations." This provision essentially outlaws the use of force by one State against another, except in very specific circumstances spelled out elsewhere in the Charter (self-defense and enforcement measures sanctioned by the Security Council). Employing mercenaries to use force against another State comes within the scope of this prohibition.

Common article 3 of the Geneva Conventions (1949)

According to this article, in any conflict, whether of international or non-international character, "persons taking no active part in the hostilities, including members of armed forces who have laid down their arms and those placed hors de combat by sickness, wounds, detention, or any other cause, shall in all circumstances be treated humanely, without any adverse distinction founded on race, colour, religion or faith, sex, birth or wealth, or any other similar criteria."

Protocol I Additional to the Geneva Conventions relating to the Protection of Victims of International Armed Conflict (1977), article 47

Article 47 of Additional Protocol I provides a definition of a mercenary.

"A mercenary is any person who:

  1. Is specially recruited locally or abroad in order to fight in an armed conflict;
  2. Does, in fact, take a direct part in hostilities;
  3. 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;
  4. Is neither a national of a Party to the conflict nor a resident of territory controlled by a Party to the conflict;
  5. Is not a member of the armed forces of a Party to the conflict; and
  6. Has not been sent by a State which is not a Party to the conflict on official duty as a member of its armed forces.

These requirements are cumulative, which means that they must all be applicable for an individual to be categorized as a mercenary."

As the purpose of the international humanitarian law is to extend rather than restrict protection, the scope of this definition is narrow in order to ensure that the loss of special protection occurs only in limited circumstances.

International Convention against the Recruitment, Use, Financing and Training of Mercenaries (1989)

The Convention establishes a range of offences that may be committed by individual mercenaries, persons recruiting, using, financing or training mercenaries, and States parties, and imposes on States parties a number of related obligations.

Article 1 keeps the definition of a mercenary contained in article 47 of the Protocol Additional I to the Geneva Conventions (see above), but expands it to cover situations other than armed conflicts, in which persons are recruited for the purpose of participating in a concerted act of violence aimed at overthrowing a Government or otherwise undermining the constitutional order of a State, or undermining the territorial integrity of a State.

In such a situation, "a mercenary is a person who:

  1. Is motivated to take part essentially by the desire for significant private gain, and is prompted by the promise or payment of material compensation;
  2. Is neither a national nor a resident of the State against which such an act is directed;
  3. Has not been sent by a State on official duty; and
  4. Is not a member of the armed forces of the State on whose territory the act is undertaken.

To commit an offence under the Convention, a mercenary must not only fall within the definition contained in article 1 but also participate directly in hostilities or in a concerted act of violence, or have attempted to do so.

An offence is also committed by any person who recruits, uses, finances or trains mercenaries, attempts to do so, or is the accomplice of a person who commits or attempts to commit an offence set forth in the Convention. This indirect offence is deemed to have been committed even where the mercenaries in question have not yet taken part in hostilities. The purpose of the direct combat requirement is to distinguish a mercenary from a military adviser.

The Convention also sets out a framework to facilitate the prosecution of offenders at the national level. It requires States to ensure that their legislation makes prosecution possible. Any alleged offender present on their territory should be taken into custody and a preliminary inquiry opened. If the person concerned is not extradited to another State for trial, the case should be submitted to the competent national authorities. Throughout the proceedings, the alleged offender should benefit from fair treatment and judicial guarantees. States should cooperate with one another in both the prevention and prosecution of offences, including through the exchange of information. Lastly, the Convention establishes a procedure for the settlement of disputes between States parties concerning the interpretation or application of the instrument.

Regional standards

Convention for the Elimination of Mercenarism in Africa (1977)

The Africa Union's Convention prohibits both mercenaries and mercenarism, which is characterized as a crime against peace and security in Africa, whether committed by an individual, a group, an association, a State or a State representative.

Article 1 defines a mercenary as "any person who:

  1. Is specially recruited locally or abroad in order to fight in an armed conflict;
  2. Does in fact take a direct part in the hostilities;
  3. 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;
  4. Is neither a national of a party to the conflict nor a resident of territory controlled by a party to the conflict;
  5. Is not a member of the armed forces of a party to the conflict; and
  6. Is not sent by a State other than a party to the conflict on official mission as a member of the armed forces of the said State."
The framework of this Convention criminalizes the sheltering, assisting, training, equipping, promoting, supporting, employing or enlisting mercenaries. The regime also criminalizes the allowing of such activities as "to be carried out in any territory under its jurisdiction or any place under its control or afford facilities for transit, transport or other operations" of mercenary forces (article 2).