The Law of State Responsibility in Relation to Border Crossings: An Ignored Legal Paradigm

Author:Louise Arimatsu
Position::Associate Fellow with the International Law Programme, Chatham House (UK)
State Responsibility in Relation to Border Crossings Vol. 89
The Law of State Responsibility in
Relation to Border Crossings:
An Ignored Legal Paradigm
Louise Arimatsu*
his article revisits the law of State responsibility to ask whether, rather
than invoking self-defense, there is a better way to conceptualize a State’s
violent engagement with a non-State actor
located in the territory of an-
other State when the latter does not consent to foreign intervention and is
itself unable or unwilling to stop the non-State actor from directing further
attacks. In posing this question my intention should not be misinterpreted
as one that seeks to identify a broader exception to the general prohibition
on the use of force; in fact, it is quite the reverse. This article proposes a
more legally coherent account of State practice that preserves an inter-State
reading of self-defense. In that process, it offers an explanation for the re-
cent statements by the International Court of Justice (ICJ) that seem to rule
out the option of invoking self-defense under Article 51 of the UN Charter
* Associate Fellow with the International Law Programme, Chatham House (UK).
Thanks to Hemi Mistry for research support on this project. The views expressed in this
article are the sole responsibility of the author and do not reflect the view of the author’s
. The term “ non-State actor” denotes any entity with the capacity to launch an
armed attack, be they organized armed groups, terrorist groups or rebels.
International Law Studies 2013
against non-State actors.
Although this stance by the ICJ has been criti-
cized for not corresponding with the recent practice of States, if Article 51
cannot be invoked to justify the use of force against a non-State actor in
the scenario described above, are there any existing laws which would per-
mit States to cross an international border lawfully?
In Part II, I argue that there are good reasons for preserving the tradi-
tional reading of Article 51, which was designed exclusively to regulate rela-
tions among States. To support this position, I identify the inherent weak-
nesses (as well as the attendant risks) embedded in the views that have
emerged in recent years to justify the use of force against non-State actors
based in the territory of a State that is unable to prevent further attacks but
is also unwilling to consent to the armed intervention by the State under
In Part III, I explore further the argument that favors extending Article
51 to non-State actors to ask why the non-State actor’s geographical loca-
tion determines the applicability of the jus ad bellum. If the answer to this
question is simply that the crossing of the border is game-changing, an ex-
planation of why this is so is warranted. If, on the other hand, there is no
compelling reason why this should be so, it raises an important question as
to whether self-defense is the most coherent legal framework within which
to conceptualize the use of force against non-State actors. And if this in-
deed is the case, how might a border be lawfully crossed?
In Part IV, I tentatively suggest that existing international law has the
potential to provide a satisfactory legal framework within which to address
these questions. In addition to the two codified exceptions to the prohibi-
tion on the use of force, there is a long tradition, demonstrated by con-
sistent State practice, that the wrongfulness of a use of force can be pre-
cluded in one, and possibly two, other exceptional circumstances found in
customary international law. International law has long recognized the right
of a State to consent to the intervention of foreign armed forces to assist it
in maintaining its internal security. Where the intervention is consensual,
. See Legal Consequences of the Construction of a Wall in the Occupied Palestinian
Territory, Advisory Opinion, 2004 I.C.J. 136, ¶ 139 (July 9) [hereinafter Wall Advisory
Opinion]; Armed Activities on the Territory of the Congo (Dem. Rep. C ongo v. Uganda),
2005 I.C.J. 168, ¶ 147 (Dec. 19) [hereinafter Armed Activities Judgment]. But see also
Judge Kooijmans’ Separate Opinion, ¶¶ 31–35, and Judge Simma’s Separate Opinion, ¶¶
713, in the Armed Activities judgment.
State Responsibility in Relation to Border Crossings Vol. 89
there is no violation of Article 2(4).
A second principle of international law
that precludes the wrongfulness of an act that would otherwise be consid-
ered a violation of the law is the plea of necessity. I suggest that it is this
customary international law principle that provides a far more coherent
basis upon which to justify the use of force against the non-State actor lo-
cated in the territory of another State that is unwilling to prevent further
I conclude by arguing that the conditions attached to necessity function
to severely restrict its availability, more so than self-defense. Thus, the crit-
ics of current State targeting policy with respect to the members of orga-
nized armed groups (OAGs) in foreign territories are no more likely to be
convinced on the facts that a robust case of necessity has been made out.
However, by contrast to self-defense, invoking necessity to justify the use
of force against an OAG in the territory of another State enables that State
to cross a border lawfully if the requisite conditions are satisfied. For the
State claiming the right to use force in such circumstances, there are further
legal hurdles thrown up by jus in bello that must be overcome before its
conduct is considered lawful.
Constituted in the aftermath of the Second World War, the primary ambi-
tion of the United Nations Charter system, as exemplified by Article 2(4),
was to prevent future war between States.
The contemporary law on the
use of force is founded on the now customary international law prohibi-
set forth in the Article, which states: All members shall refrain in their
international relations from the threat or use of force against the territorial integri-
Consent functions to negate what is otherwise a wrongdoing.
. The Preamble of the Charter opens with the declaration,
We the Peoples of the United Nations determined to save succeeding g enerations from
the scourge of war, which twice in our lifetime has brought untold sorrow to mankind, . . .
and for these ends to practice tolerance and live together in peace with one another as
good neighbours, and to unite our strength to maintain international peace and security,
and to ensure, by the acceptance of principles and the institution of methods, that armed
force shall not be used, save in the common interest, . . . have resolved to combine our ef-
forts to accomplish these aims.
. Military and Paramilitary Activities in and Against Nicaragua (Nicar. v. U.S.), 1986
I.C.J. 14, ¶ 190 (June 27) [hereinafter Nicaragua Judgment].

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