Due Diligence in International Law

Before international human rights law came into being, the protection of individuals under international law was governed by the minimum standard for the treatment of aliens. The exercise of state sovereignty with extraterritorial consequences was subject to the international law obligation of due diligence, the no harm principle or the principle sic utere tuo ut alienum non laedas. This contribution determines to what extent these obligations can be relied upon today to advance extraterritorial obligations of states towards migrants. Crucially for this purpose, the due diligence obligation is not limited to individuals within the jurisdiction of a State. Rather, States must ensure that activities within their jurisdiction do not cause serious harm to individuals in the territory of another State or to common interests of the international community.

Responsibility for harmful extraterritorial effects of State action or inaction

The international obligation of due diligence rule is set out in the arbitral awards rendered in the Las Palmas and Trail Smelter arbitration cases, respectively of 1928 and 1941. In the Las Palmas case, opposing the United States of America to the Netherlands, the arbitrator considered that territorial sovereignty has as a corollary the duty to protect the rights of other States, and in particular “the rights which each State may claim for its nationals in foreign territory” (p. 839). In the 1941 Trail Smelter case between the United States and Canada, the Tribunal held that no State has the right to use or permit the use of its territory in a manner that causes serious injury to individuals in the territory of another State:

“… under the principles of international law, … no State has the right to use or permit the use of its territory in such a manner as to cause injury by fumes in or to the territory of another or the properties or persons therein, when the case is of serious consequence and the injury is established by clear and convincing evidence.” (p. 1965)

Due diligence thus obliges States in respect of what they do or permit on their own territory. It is debated whether it is of general application in international law or ancillary to specific primary rules, but it indisputably applies to the treatment of aliens.

It is extraterritorial in that it aims at preventing damage outside the territory, either to the territory of another State or to the properties or persons in that foreign territory. And importantly, as evidenced by the Trail Smelter formula, the connecting factor between State action or inaction and the external event is one of causation, or effect. This was subsequently confirmed by Principle 21 of the 1972 Stockholm Declaration on the human environment, according to which States must not “cause damage” beyond their territory. It is also inherent in the International Court of Justice’s dictum in Legality of the threat or use of nuclear weapons that States must ensure that “activities within their jurisdiction or control respect the environment of other States or of areas beyond national control” (§29). It follows that the responsibility of a State pursuant to the due diligence obligation is not dependent on that State having jurisdiction over the injured individual. As it stems from the law of coexistence between sovereign States, the due diligence obligation originally aims at preventing States from encroaching on the jurisdiction of other States. In this context, what triggers the due diligence obligation is not that an individual suffering damage is within the jurisdiction of the State causing that damage. To the opposite, the obligation emerges where an individual is within the jurisdiction of another sovereign State. Therefore, what matters is the existence of a causal link between a fact of the State and the harm sustained by an individual, irrespective of whether that individual falls under the jurisdiction of the State (in the narrow sense of some human rights instruments).

Due diligence with respect to community interests

The due diligence principle as it was formulated in the first half of the 20^th Century was meant to protect States, territory and population as assets of the sovereign State, against foreign harmful interference. It would allow for diplomatic protection by the State of an injured individual’s nationality. However, it would not readily allow for the protection of migrants fleeing their home State and bobbing on the high seas in an unseaworthy ship.

Since then, however, the obligation has evolved in line with the evolution of international law towards a law of cooperation and of protection of community interests. As early as 1972, it was stated in Principle 21 of the Stockholm Declaration on the human environment that States must not cause damage to the environment of other States “or of areas beyond the limits of national jurisdiction”. In its Advisory Opinion of 1996 on the Legality of the threat or use of nuclear weapons (which, though not legally binding, provides an authoritative statement on the lex lata), the International Court of Justice confirmed the obligation of States to ensure that activities within their jurisdiction and control respect the environment of other States “or of areas beyond national control” (at §29). This is an erga omnes obligation in the general interest of the international community of States.

Humans are entitled to the same protection as the environment. As stated by the International Court of Justice in the Barcelona Traction case, “the principles and rules concerning the basic rights of the human person” generate erga omnes obligations which are by their very nature the concern of all States (§§33-34). It follows that States have a due diligence obligation under international law to act and abstain from acting, in such a manner that no injury be caused to individuals irrespective of their nationality (their belonging to another State) and irrespective of where they are located.

The standard of protection

The substantive scope of the due diligence obligation is different from that under international human rights treaties to respect, protect and fulfil human rights. Due diligence sets a lower standard of protection. In environmental matters, due diligence is limited to the prevention of “serious consequences” (in the terms of Trail Smelter) or “significant damage” (as stated by the International Court of Justice in Pulp Mills on the River Uruguay, §101). Likewise, in international economic law, due diligence concretizes in the so-called minimum standard for the treatment of aliens. As illustrated by Article 1105 of the North American Free Trade Agreement, the arbitral award in Mondev, and Article 14.6 of the United States – Mexico – Canada Agreement, this customary law regime has not been abolished by modern human rights law. Rather, treaty practice suggests that the due diligence obligation with respect to individuals is limited to manifest or gross violations of fundamental rights. It would, for instance, not provide for non-discriminatory treatment in all areas covered by human rights treaties but would protect against “targeted discrimination on manifestly wrongful grounds, such as gender, race, or religious belief” (e.g., CETA Article 8.10.2.d).

A more generous approach is suggested by a dictum in the Diallo case, where the International Court of Justice stated that diplomatic protection was originally limited to alleged violations of the minimum standard of treatment of aliens, but had “subsequently widened to include, inter alia, internationally guaranteed human rights” (§39). However, this broadened scope of diplomatic protection is arguably limited to situations where the individual concerned is within the responsible State’s jurisdiction or control. In the alternative, such broader protection might be limited to the obligation to respect or extends to the obligations to protect and fulfill.

This shows that protecting migrants against externalization policies on the basis of the due diligence obligation of general international law does not amount to circumventing the limits to human rights treaty protection, or to unduly expanding that protection. Protection under the due diligence obligation may be broader in scope because it is causation-based as opposed to jurisdiction-based. But it is more limited in scope as far as the substantive standard of protection is concerned.

Right-holders and remedies

The due diligence obligation under general international law does not, of course, give access to the remedial mechanisms specific to human rights treaties. What is more, due diligence originally conferred rights to States rather than directly to individuals. This raises two distinct questions. The first question is whether individuals can invoke the due diligence obligation as a basis for a legal claim, or whether only States can do so.  If the obligation can in principle be invoked by individuals, the second question is whether this remains the case when the individuals’ State of nationality acquiesces to the violation. Both these issues are illustrated by the jurisprudence of the United States Supreme Court. In Alvarez-Machain, a Mexican national was kidnapped in Mexico by a de facto agent of the United States to be judged in the United States. The court of appeals held that the kidnapping affected the jurisdiction of United States courts to try the suspect, given that Mexico had protested the violation of its territorial integrity (p. 667). The Supreme Court however ruled that the jurisdiction of United States courts was unaffected. While the suspect’s abduction was arguably “shocking” and in violation of general international law principles, the decision of whether he should be returned to Mexico may be a matter for the Executive Branch, but there was no violation of the extradition treaty between the United States and Mexico on which the courts could adjudicate (p. 669).

But international law has been clarified since then. In the Diallo case, the International Court of Justice referred to the diplomatic protection of “Mr. Diallo’s rights as an individual” without differentiating between the minimum standard for the treatment of aliens and internationally guaranteed human rights (§§34, 39). In these circumstances, an individual’s rights under customary international law qualify as having ‘direct effect’ where this is required by domestic law – as it is the case in Belgium – as a condition to trigger the State’s tort liability or to invalidate an administrative act.

In addition, the justiciability of a violation of the minimum standard of treatment of individuals cannot depend on the protest or lack of acquiescence by the State of nationality of the victim. The obligation is erga omnes in nature, so that a State breaching that obligation can be held responsible by any other non-injured State,, as provided in Article 48 of the ILC Articles on State Responsibility and the jurisprudence of the International Court of Justice. Compliance with the obligation is therefore not in the hands of the State of nationality.

Conclusion

Irrespective of their obligations under international human rights treaties, all States have the obligation under customary international law not to cause serious harm to individuals outside their territory. They have an erga omnes obligation to respect the minimum standard for the treatment of individuals, no matter where they are located. This obligation may be narrower than under international human rights instruments, as it is arguably limited to gross violations of human rights. But it is also broader than under many instruments, as it does not depend on the individuals concerned being within the jurisdiction of the State concerned in a narrow sense, i.e. within the State’s direct control.