The Republic of Nicaragua v.
The United States of America
ICJ June 27, 1986.
The facts
• July 1979
• 1981
• 1983
• 1984
• 9 April 1984
Sandinista government in
Nicaragua
Nicaragua supported armed
groups in El Salvador
USA fund for the Contras
USA laid mines in Nicaraguan
ports; infringement of Nicaraguan
air space; economic measures
against Nicaragua
Nicaragua’s claim at the ICJ
The facts
Arguments – Nicaragua:
• Violations of treaty obligations (supplying
military paramilitary actions)
• Violations of international law (sovereignty,
use of force, intervention)
• Reparations
The facts
Arguments – USA:
• Nicaragua supported armed groups
• Cross border military attacks
• Collective self defence
Why Customary Law was
Important in this Case
• Before evaluating the case on the merits, the
Court had to decide whether the U.S.
reservation stripped the Court of its jurisdiction.
• The reservation excluded from Article 36 of the
Statute of ICJ “disputes arising under a
multilateral treaty, unless (1) all parties to the
treaty affected by the decision are also parties to
the case before the Court, or (2) the United
States of America specially agrees to
jurisdiction.”
Why Customary Law was
Important in this Case
• The Court concluded that the reservation is
applicable in this case because
– U.S. did not specially agree to the jurisdiction in this
case, and
– Parties to the treaty affected by the decision were not
all parties before the court. Parties to the dispute
included United States and Nicaragua. However, U.S.
claimed it was acting in collective self-defense on
behalf of El Salvador. El Salvador was not a party
before the Court. The Court determined El Salvador
would be affected by its judgment.
Why Customary Law was
Important in this Case
• As a result, the Court determined that the
reservation barred it from applying the
multilateral treaties to this case.
• But the Court did not stop there, however.
• The Court viewed the reservation as a limitation
on the type of law that the court could apply
(multilateral treaties), not as a limitation on its
overall jurisdiction to hear the case.
• Thus other sources of law under Art. 38 of the
Statute of the ICJ were still applicable, including
customary international law.
Why Customary Law was
Important in this Case
• U.S. argued that customary rules whose content
is identical to that of the treaties cannot be
applied due to the U.S. reservation.
• The Court rejected this and held that just
because a treaty incorporates customary
international law, it does not deprive the
customary law of its applicability distinctly from
the treaty.
• Thus according to the Court, treaties and
customary law have independent existence
and apply separately, even when both deal
with the same subject matter.
Why Customary Law was
Important in this Case
• Court states “. . . Even if the customary norm and the
treaty norm were to have exactly the same content, this
would not be a reason for the Court to hold that the
incorporation of the customary norm into treaty-law
must deprive the customary norm of its applicability
as distinct from that of the treaty norm . . . . More
generally, there are no grounds for holding that when
customary international law is comprised of rules
identical to those of treaty law the latter “supervenes” the
former, so that the customary law has no further
existence of its own.” I.C.J. Reports 1986, p. 94-95,
para. 177 (emphasis added).
Why Customary Law was
Important in this Case
• Example:
If two States (A and B) are subject to a
bilateral treaty and State A breaches, State
B would no longer be obligated to comply
with that treaty. However if there was also
customary law applicable to the situation,
the two States would still have to abide by
it, independently of the treaty.
Which rules of customary
international law were addressed in
the case?
• Not to intervene in the affairs of another State.
• Not to use force against another State. Art. 2(4) UN
Charter
• Right to self-defence. Art. 51 UN Charter
• Not to violate its sovereignty.
• Collective counter-measures in response to conduct not
amounting to armed attack.
Opinio Juris and State Practice
• Once the Court had decided to apply customary law, it
had to ascertain which rules of customary law were
relevant to this case.
• Therefore, the Court considered whether a customary rule
exists in the opinio juris of States, and satisfy itself that it
is confirmed by practice.
• It is important to really check the material of customary
international law in the actual practice and opinio juris of
States. It doesn’t matter if these rules have already been
collected by several treaties or any other intruments.
Opinio Juris and State Practice
• The Court also noted that both Nicaragua and US had a
considerable degree of agreement as to the content of
the customary international law related to the non-use of
force and non-intervention.
• But, the fact that States declare their recognition of
certain rules is not sufficient for the Court to consider
these as being part of customary internt. law and as
applicable as such to those States. The Court must not
disregard the rol played by “general practice”. The Court
must satisfy itself that the existences of the rule in the
opinio juris of States is confirm by practice.
Opinio Juris and State Practice
• Thus, the Court held that the attitude of the parties and
States towards certains General Assembly Resolutions
could be indicative of opinio juris. (189. As regards the United
States in particular, the weight of an expression of opinio juris can
similarly be attached to its support of the resolution of the Sixth
International Conference of American States condemning
aggression (18.02.28) and ratification of the Montevideo Convention
on Rights and Duties of States (26.12.33).
• Controversy:
Some scholars say that the Court should first look to
state practice and not to opinio juris. And since the Court
in this case looked to opinio juris without emphasizing
state practice, it got it backwards.
Opinio Juris and State Practice
• Some others say that it is not normally even necessary
to prove the existence of opinio juris when you have firm
evidence of state practice. In the Nicaraguan case the
ICJ demanded very little evidence of actual state
practice, where it saw clear evidence of opinio juris. It
found evidence of opinio juris by looking to the General
Assembly resolutions. (Int. Law Association – London Conference
2000)
• If there is enough evidence of state practice, opinio juris
is not always necessary, and usually if it does exist,
courts use it only to confirm the existence of state
practice as indicative of customary law.
• But, where there is little evidence of state practice, court
will make up for that with greater evidence of opinio juris
and vice versa.
How the ICJ Address State Practice
and Opinio Juris
1. Use of Force
• Party Agreement
• General Assembly Resolution 2625 (XXV)
• Resolution of The Sixth International Conference
of American States Concerning Aggression 18
Feb 1928
• Montevideo Convention on the Rights and
Duties of States 26 December 1933
How the ICJ Address State Practice
and Opinio Juris
2. Self Defence
• Party Agreement
• UN Charter Article 51
• General Assembly Resolution 2625 (XXV)
• General Assembly Resolution 3314 (XXIX)
• Charter of Organisations of American
States
• International Treaty of Reciprocal
Assistance 1947
How the ICJ Address State Practice
and Opinio Juris
3. Non-intervention
• Numerous declarations and resolutions
• Corfu Channel (Merits) United Kingdom v
Albania 1949 ICJ Reports 4
How the ICJ Address State Practice
and Opinio Juris
4. Collective counter-measures in response to
conduct not amounting to armed attack
• Counter-measures is an exemption of non-intervention
principle;
• Counter-measures is analogous to the right of selfdefence in the case of armed attack;
• ICJ: “armed attack must be understood as including not
merely action by regular armed forces across an
international border, but also ‘sending by or on behalf of
a State of armed bands, groups, irregulars or
mercenaries, which carry out attacks of armed force
against another State of such gravity as to amount to an
actual armed attack conducted by regular forces, or its
substantial involvement therein.”
How the ICJ Address State Practice
and Opinio Juris
5. State sovereignty
The concept of sovereignty extends to the internal waters
and territorial sea of every State and to the airspace above
its territory:
– Art. 2(1) of the UN Charter;
– Art. 1 of the Chicago Convention on International Civil Aviation
(1944);
– Geneva Convention on the Territorial Sea (1958);
– UN Convention on the Law of the Sea (1982).
– Laying of mines by another State is infringement of the freedom
of communications and of maritime commerce.
How the ICJ Address State Practice
and Opinio Juris
6. Humanitarian law
• A breach of the principles of humanitarian law
underlying the specific provisions of Hague Convention
(Art. 3 and 4);
• United States commited violation of Art. 3 of the fourth
Geneva Convention;
• The conflict between Contras forces and those of the
Government of Nicaragua is an armed conflict which is
"not of an international character";
• Obligation on the United States Government, in the
terms of Art. 1 of the Geneva Convention is to
"respect" the Conventions and even "to ensure
respect" for them "in all circumstances" (general
principle of humanitarian law)
How did the ICJ address differences in
opinion regarding the content of the
substantive rule(s)?
• The court found in its legal verdict that the US was “in
breach of its legal obligations under customary
international law not to use force against another state”,
“not to intervene in its affairs”, “not to violate its
sovereignty”, “not to interrupt peaceful maritime
commerce”, and “in breach of its obligations under Article
XIX of the Treaty of Friendship, Commerce and
Navigation between the Parties signed at Managua on
21 January 1956”.
• It said that it was not necessary that the practice in
question had to be “in absolutely rigorous conformity”
with the purported customary rule.
How did the ICJ address differences in opinion
regarding the content of the substantive
rule(s)?
• The court continued: In order to deduce the existence of
customary rules, the court deems it sufficient that the
conduct of states should, in general, be consistent with
such rules, and that instances of state conduct
inconsistent with a given rule should generally have
been treated as breaches of that rule, not as indications
of the recognition of a new rule.
• If a State acts in a way that is incompatible with a
recognized rule, but then defends its action by trying to
appeal to an exception to that rule, then whether or not
the State's conduct is in fact justifiable on that basis, the
significance of that attitude is to confirm rather than to
weaken the rule.