Gabcikovo-Nagymaros Project (Hungary v Slovakia)
Rule established
A party cannot unilaterally terminate a treaty on grounds of necessity or fundamental change of circumstances unless strict customary law conditions are met; the treaty continues unless lawfully terminated.
Facts
- Hungary and Czechoslovakia concluded a 1977 treaty to build a system of locks and dams on the Danube
- In 1989, Hungary suspended works citing ecological concerns (impact on drinking water and biodiversity)
- In 1992, Hungary purported to terminate the treaty
- Slovakia (successor to Czechoslovakia) proceeded with a unilateral variant of the project (Variant C), diverting the Danube
- Hungary invoked impossibility of performance, fundamental change of circumstances, and the state of necessity as grounds for termination
- Slovakia argued the treaty remained in force and Hungary was in breach
Issue
- Whether Hungary was entitled to suspend and terminate the 1977 treaty on grounds of ecological necessity, impossibility, or fundamental change of circumstances, and whether Slovakia's unilateral Variant C was lawful.
Held
- Hungary was not entitled to terminate the treaty
- The conditions for invoking necessity under customary law were not satisfied (the peril was not imminent and grave; Hungary contributed to the situation)
- Fundamental change of circumstances (rebus sic stantibus) was not established (environmental concerns were not unforeseen; they did not radically transform obligations)
- Impossibility of performance failed (the treaty could still be performed, just in a modified way)
- Slovakia's Variant C was also unlawful as a disproportionate unilateral act
Ratio Decidendi
A state may only invoke necessity as a ground precluding wrongfulness if the act is the sole means of safeguarding an essential interest against a grave and imminent peril and does not seriously impair the essential interest of the other state. Fundamental change of circumstances requires that the change be unforeseen, relate to an essential basis of consent, and radically transform the extent of remaining obligations. These are strict, exceptional defences and were not met here.
How to use it in an exam
- The richest single authority for PIL-3.5 treaty termination questions
- Covers necessity, rebus sic stantibus, impossibility, and countermeasures in one judgment
- Deploy in Part B essays on grounds for terminating or suspending treaties
- Pair with Reservations to Genocide Convention (1951) for treaty law questions
- Key line: "The state of necessity is a ground recognised by customary international law for precluding the wrongfulness of an act not in conformity with an international obligation, but it can only be accepted on an exceptional basis."
Source
Source: ICJ Reports 1997, p 7; verified via ICJ database
This is an educational summary, not the judgment itself. Cite the reported version in professional or academic work.