Customary International Law: Treaty Modifications Explained

Treaties are written conventions that formally establish rules that are binding on states that have consented to be bound by them. Customary international law, on the other hand, is derived from a general practice accepted as law. This raises the question of whether customary international law can modify a treaty. This paragraph will explore the relationship between customary international law and treaties and discuss the potential for customary international law to alter or amend treaty provisions.

Customary international law and treaty law as sources of international law

Customary international law and treaty law are both sources of international law. Treaties are written conventions in which states formally establish certain rules and are binding only on those states that have expressed their consent to be bound by them, typically through ratification. On the other hand, customary international law arises from "a general practice accepted as law", independent of treaty law. This customary law can be found in official accounts of military operations, military manuals, national legislation, and case law.

Customary international humanitarian law (IHL) is particularly important in today's armed conflicts, as it fills gaps left by treaty law and strengthens the protection of victims. The Statute of the International Court of Justice recognises both treaty law and customary international law as binding sources of international law. This is further evidenced by the application of customary international law by national and international courts and tribunals.

While treaties are binding on states, a treaty is void if, at the time of its conclusion, it conflicts with a peremptory norm of general international law. Such a norm is accepted and recognised by the international community of states as a whole and can only be modified by a subsequent norm of general international law of the same character. Additionally, a state may not invoke the provisions of its internal law to justify its failure to perform a treaty.

Customary international law and treaty law can coexist and complement each other. According to the Vienna Convention Law Treaties, a rule set forth in a treaty can become binding upon a third state as a customary rule of international law. This indicates that customary international law can potentially modify or extend the application of a treaty to additional states beyond the original signatories. However, it is important to note that a treaty may also be amended by agreement between the parties, as provided in the treaty or through established procedures.

Treaties are binding only on consenting states

The Vienna Convention on the Law of Treaties, which governs the formation and operation of treaties, upholds the principle of state consent. Article 46 of the Convention specifies that a state cannot invalidate its consent to be bound by a treaty due to a violation of its internal law unless the violation is manifest and concerns a fundamental rule. Additionally, Article 54 of the Convention outlines that the termination of a treaty or withdrawal of a party requires the consent of all parties, further emphasising the importance of state consent.

The binding nature of a treaty is limited to the states that have agreed to it. This is in contrast to customary international law, which can bind all states. Customary international law derives from "a general practice accepted as law" and exists independently of treaty law. It fills gaps left by treaty law and strengthens the protection offered to victims in today's armed conflicts. While treaties are specific written conventions that formally establish rules between consenting states, customary international law arises from accepted practices reflected in military manuals, national legislation, and case law.

It is worth noting that treaties and customary international law are both recognised as sources of international law. They coexist and interact in a complex legal landscape. While treaties are binding only on consenting states, customary international law can modify or revoke certain rights and obligations within a treaty for those states. This dynamic relationship between treaty law and customary international law ensures the flexibility and adaptability of international legal norms to address emerging challenges and changing circumstances.

Customary international humanitarian law (IHL) and its importance in armed conflicts

Customary international humanitarian law (IHL) is of paramount importance in today's armed conflicts. IHL, also known as the laws of armed conflict, is a branch of international law that aims to mitigate the impact of armed conflict by protecting non-combatants and restricting the means and methods of warfare available to combatants. It is inspired by humanitarian considerations and the goal of reducing human suffering.

IHL is based on the Fourth Geneva Convention of 1949, which focuses on protecting civilians in conflict, and the Additional Protocols of 1977 and 2005. While many aspects of IHL are now recognised as customary international law, they are frequently violated by warring parties. These violations include attacks on relief organisation buildings, hijacking of vehicles and convoys, assaults on hospitals and schools, and violence against staff, all of which hinder the delivery of life-saving assistance to millions of people.

The importance of customary IHL lies in its ability to fill the gaps left by treaty law and strengthen the protection of victims of armed conflict. Customary IHL is derived from "a general practice accepted as law", which can be found in official records of military operations, military manuals, national legislation, and case law. It operates independently of treaty law and is binding on states, as recognised in the Statute of the International Court of Justice.

IHL establishes rules and principles that govern the conduct of warfare, defining the responsibilities of belligerent nations, neutral nations, and individuals engaged in warfare. It includes provisions such as the principle of distinction, which mandates the protection of civilian populations and objects from military operations, and the principle of humane treatment, prohibiting violence, cruel treatment, torture, and other inhumane acts against non-combatants.

The EU, as one of the world's largest humanitarian donors, has demonstrated a strong commitment to promoting compliance with IHL. All EU countries have ratified the four Geneva Conventions and their Additional Protocols, and the EU has adopted guidelines to promote compliance with IHL, emphasising its importance in external actions. The European Commission's Civil Protection and Humanitarian Aid Operations department (ECHO) actively promotes global adherence to IHL and humanitarian principles.

Treaties can be amended by agreement between parties

Treaties are written conventions in which states formally establish binding rules and are only binding on those states that have expressed their consent to be bound by them, usually through ratification. Treaties can be amended by agreement between the parties, as outlined in the Vienna Convention Law of Treaties. The convention states that any proposal to amend a multilateral treaty between all parties must be notified to all contracting states, and each state has the right to withdraw its consent to be bound by the treaty.

The convention also specifies that the termination of a treaty or the withdrawal of a party may occur in two ways: in conformity with the provisions of the treaty or at any time by consent of all parties after consultation with the other contracting states. This highlights the dynamic nature of treaty law, where the agreement between parties is essential, and modifications or withdrawals can be made through a collaborative process.

Customary international humanitarian law (IHL), on the other hand, consists of rules that come from "a general practice accepted as law" and exist independently of treaty law. It fills the gaps left by treaty law and strengthens the protection offered to victims in today's armed conflicts. Customary IHL is derived from practices found in official accounts of military operations, military manuals, national legislation, and case law.

While both treaty law and customary international law are recognised as sources of international law, they serve different purposes. Treaty law establishes specific rules agreed upon by consenting states, while customary international law fills in the gaps with generally accepted practices. In summary, treaties play a crucial role in international law by providing a framework for binding agreements between nations, and they can be amended through the agreement of the involved parties as outlined in the Vienna Convention Law of Treaties.

Treaties are void if they conflict with a peremptory norm of general international law

Treaties are a written convention in which states formally establish certain rules and are binding only on those states that have expressed their consent to be bound by them, usually through ratification. Customary international law, on the other hand, is derived from "a general practice accepted as law". It fills the gaps left by treaty law and strengthens the protection offered to victims. Both treaty law and customary international law are sources of international law and are binding.

A peremptory norm (also called jus cogens) is a fundamental principle of international law that is accepted by the international community of states as a norm from which no derogation is permitted. There is no universal agreement on which norms are jus cogens or how a norm reaches that status. However, it is generally accepted that jus cogens bans certain acts such as genocide, maritime piracy, slavery, and torture. Peremptory norms may not be violated by any state, including through international treaties.

A treaty is void if, at the time of its conclusion, it conflicts with a peremptory norm of general international law. This is outlined in Article 53 of the Vienna Convention on the Law of Treaties. If a new peremptory norm of general international law emerges, any existing treaty that conflicts with that norm becomes void and terminates. In such a case, the parties must eliminate any consequences of acts performed in reliance on the provision conflicting with the peremptory norm and bring their mutual relations into conformity with the peremptory norm.

The Nuremberg Trials marked the first enforcement of international norms upon individuals, and it is now widely accepted that peremptory norms can define criminal offences that are enforceable against states and individuals. Some examples of peremptory norms include the prohibition of torture, the impermissibility of a state acquiring territory through war, and the prohibition of crimes against humanity.

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