This dissertation employs the doctrinal method of research to appraise the doctrine of Self defence as one of the fundamental principles of International law, and as one of the exceptions to the prohibition on the use of force. To this end, this dissertation centers on Article 51 of the United Nations Charter which provides for the right of self defence in International law. The dissertation contends that the provisions of Article 51 have generated some controversies among scholars of International law. These controversies have tended to obscure the scope of self defence in International law. The major problem of this research is that it is not clear whether Article 51 has abrogated or preserved the doctrine of anticipatory Self defence in Customary
International law. This problem has been complicated by the use of the phrases ‘inherent right of individual or collective self defence’ and ‘armed attack’ in Article 51. The question therefore is that ‘does international law expect a State to do nothing where it is a target of an imminent attack’? The objective of this dissertation therefore is to examine the relationship between Article 51 and rules of customary International Law, and the circumstances in which the right of self defence can be exercised. The dissertation makes some findings by submitting that the doctrine of preemptive Self defence is contrary to Articles 2(4) and 51 of the Charter which prohibits unilateral use of force. Furthermore, both Article 51 and customary international law provide different rules for the exercise of the right of self defence .The writer suggests that there is urgent need for an amendment of Article 51 to bring it in line with current global challenges to global security. The phrase ‘armed attack’ should be well defined and the concept of collective self defence should be deleted from Article 51.  

Background to the Study 

 The doctrine of self-defence is one of the fundamental principles of International law.  The doctrine of self defence is common to all systems of law, and generally, as a legal concept, the   function and scope of Self-defence vary with the level of development of each legal system. Thus, International law which is characterized by lack of specialized machinery for the enforcement of International law and protection of the rights of member states has vested the individual member states the right to use force for the protection of certain essential rights. 
        However, as International law advances, as its processes of enforcement and protection become more effective, the tendency is to allocate duty of protection to a centralized authority such as the United Nations Security Council, and to restrict the right of unilateral action by individual member states. However, no matter how effective the means of protection afforded by the centralized authority is, it will be necessary, for the protection of certain essential rights, and interests of the state to invest the states with   the right of self defence until the enforcement machinery of the United Nations (UN) comes to their aid.  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-defence. This is the justification of Self-defence in International law.

In the United Nations system characterized by a decentralized machinery of its legal system, the enforcement of International law and the protection of rights recognized by International law is, traditionally, a task delegated to the individual members, the sovereign states. Naturally, the right of self-defence in international law features as the basic and fundamental right of every member state. Within the last fifty years, international community has moved towards a degree of centralization hitherto unknown; and with that development the prohibition of individual use of force has come pari pasu.Thus, the need to define the right of self-defence with some precision arises from this development, for, as the main exception to the general prohibition of force, the right of self-defence if left undefined and unregulated could virtually deny the prohibition on the use of force any real meaning.

 It is against this backdrop therefore that the writer‟s interest to research in this field is generated noting the fact that the concept of self-defence in   international law   entails certain essentials such as „necessity‟, „proportionality‟, and „Immediacy‟. Article 51 of the United

Nations Charter defines self-defence in the following terms:

Nothing in the present Charter shall impair the inherent right of individual or collective self-defence 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-defence 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 action as it deems necessary in order to maintain or restore international peace and security.