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Self defense in international law refers to the inherent right of a State to use force in response to an armed attack or imminent threat of attack directed against a state. The concept of self defense is also used in criminal law as a defense to justify a necessary and proportionate use of force against an unlawful attack. The right to use force in the defense of oneself or another against unjustifiable attack has existed from time immemorial. The doctrine of self defense is common to all systems of law and generally, the scope and function of self defense vary with the level of development of each legal system. The doctrine of self defense is one of the most fundamental principles of international law. International law which is known for its lack of specialized machinery for the enforcement of international law has vested in individual member states the right to use force for the protection of certain essential rights. [1]

Thus, International Law has provided and established a centralized authority such as the United Nations Security Council for the enforcement and protection of certain essential rights and to restrict the right of unilateral action by individual member states. However, no matter how effective the central authority is, it will be pertinent for the individual member states, for the interest states, to be vested with the right of self defense until the enforcement machinery of the United Nations comes to their aid. [2] It is difficult to envisage a legal system in which the prohibition of recourse to force has no exception in the form of the doctrine of self defense. This is the justification of self defense in International law.

Humanity has always recognized that individuals should have the right to defend themselves from violence. In the international circle, this basic normative intuition is codified for states in the United Nations Charter Article 51. Article 51 [3] is an exception to the Charter’s general prohibition on the use of force found in Article 2(4). [4] The prohibition to the use of force is the heart of the Charter, given that the most fundamental aim of the Charter and the United Nations organization created by the Charter is to “save succeeding generations from the scourge of war.” It stands to reason that any right to use force as an exception to the general prohibition on resort to force will be narrow. Thus, the need to define the right of self defense with some precision arises from this development, for, as the main exception to the general prohibition of force, the right to self defense is left undefined and unregulated could virtually deny the prohibition on the use of force real meaning. Article 51 [5] permits a state to act in unilateral or collective self defense only if an armed attack occurs. Article 51 of the United Nations Charter [6] defines self defense as:

Nothing in the present Charter shall impair the inherent right of individual or collective self defense if an armed attack occurs against a Member of the United Nations, until the Security Council has taken measures necessary to maintain international peace and security. Measures taken by Members in the exercise of this right of self defense shall be immediately reported to the Security Council and shall not in any way affect the authority and responsibility of the Security Council under the present Charter to take at any time such actions as it deems necessary in order to maintain or restore international peace and security.

The United Nations Charter was drafted at the end of World War II, when confidence in military force was certainly low and commitment to ending the use of force was high. Fifty years later, perhaps frustrated by the lack of success with other means, writers in the international community have moved towards a degree of centralized hitherto unknown and with that development, the prohibition of individual use of force has come pari pasu. [7]

The inclusion of the above provision in the United Nations Charter is significant in two main aspects. In the first instance, it strongly states that forcible measures, other than self defense, which were lawful prior to the Charter, have been made unlawful and do not survive its adoption and entry into force. [8] This is due to the fact that unlike the right of self defense, such forcible measures such as reprisals and wars are not validated by the provision of the Charter. Secondly, the general words used in Article 51 introduces a new normative dimension to the lawful exercise of the right of self defense whereby treaties, alongside the established principles of customary international law may now be used to govern the lawful exercise of any self defense action. [9]

The right of self defense is not an open-ended right. To be a valid act under international customary law, as set down by the classic formulation by the United States in the 1837 Caroline incident, it is generally required to conform with certain conditions governing the right of self defense and these conditions are ‘necessity’, ‘proportionality’ and ‘immediacy’. [10] These conditions are in addition to the condition stipulated in Article 51 of the United Nations Charter. Thus, self defense is subject to certain conditions against which the validity of any act of self defense is tested.

Therefore, this work identifies the challenges of the present practice, proffering viable measures to ensuring an effective understanding of the doctrine and practice of self defense international law.


This research is to appraise the doctrine of self defense as one of the fundamental principles of international law and as one of the exceptions to the use of force. There is a wide range of disagreements on the circumstances in which states can resort to force in self defense. The problem of this research is centered on Article 51 of the United Nations Charter which provides for the right to self defense under international law. The provisions of Article 51of the United Nations Charter has some controversies among international law scholars. These controversies have made the scope of self defense under international law very unclear. This study seeks to answer the following questions:

The aim of this research is to examine and shed more light on the doctrine of self defense in international law so that the rules governing the exercise of self defense can be made transparent. Misconception of the rules of self defense in international law has led some states to use force even where there is no justification. Therefore, the objective of this dissertation is:

  • To examine the legality of anticipatory and preventive self defense in contemporary international law.
  • To examine the extent to which self defense can be exercised against non-state actors.
  • To examine the legal consequences for the violation of Article 51 of the United Nations Charter.
  • To proffer recommendations where necessary.

The scope of this research is limited to the doctrine of self defense in international law as well as the limits to the exercise of the right to self defense.


Although there are many methods of research available which can be employed to gather information and facts on this study, this dissertation is based on doctrinal method of research. The doctrinal method will involve the use of primary and secondary documents. The primary documents include the Charter, treaties and decisions of the International Court of Justice and International Military Tribunal whereas secondary documents involve the use of books, journals, articles and newspapers that have been published. It is believed that this research method will shed more light and put the concept in proper context.


Chapter one of this work is on the General Introduction. Here, the doctrine of self defense under international law is introduced. The statement of the problem necessitating the study is stated. Then this is followed by the aims and objectives of the study, and the scope of the study dealing with the particular area of international humanitarian law. There is also the statement of the research methodology.

Chapter two deals with the conceptual clarification of key terms. These terms are self defense, war, terrorism, use of force, collective defense, customary international law. These concepts are pertinent in understanding the doctrine of self defense under international law.

Chapter three of this research examines the development and origin of self defense, the origin and interpretations of Article 51of the United Nations Charter, the rights for which self defense is permissible, means of protection, conditions of self defense and categories of self defense.

Chapter four deals with the limits to right of self defense under international law. Chapter five is the concluding chapter. It summarizes the whole work. Chapter five comprises of summary, findings on the problem identified in the course of this research and then the recommendations and suggestions are proffered on how to solve the problem of this research.

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