The International Court of Justice is the principal judicial organ of the United Nations. The Court has a dual role: to settle in accordance with international law the legal disputes submitted to it by States, and to give advisory opinions on legal questions referred to it by duly authorized international organs and agencies. The Court is composed of 15 judges elected to nine-year terms of office by the UN General Assembly and Security Council sitting independently of each other. It may not include more than one judge of any one nationality. The Members of the Court do not represent their governments but rather are independent magistrates. When the Court does not include a judge possessing the nationality of a State party to a case, that State may appoint a person to sit as a judge ad hoc for the purpose of the case. . This essay seeks to explain how effective the ICJ is in treating international disputes with reference to cases such as Nicaragua vs. USA, Palestinian Wall Advisory Opinion and the Legality of the Threat or Use of Nuclear Weapons, in addition this essay would explain how effective the UN been with regards to the use of force in International Law. In 1984, Nicaragua (plaintiff) brought suit against the United States (defendant) charging violations of customary and treaty law as a result of the United States’ military and paramilitary activities within Nicaragua. Specifically, Nicaragua alleged the United States violated Article 2, paragraph 4 of both the United Nations Charter and customary international law by committing attacks on oil pipelines, storage and port facilities, and Nicaraguan air space; as well as training, arming, equipping, financing and supplying counter-revolutionary forces seeking to overthrow the Nicaraguan government. The United States withdrew from the proceedings, but noted its position that Nicaragua had supplied arms and other support from its territory to armed opposition to the government of El Salvador. The United States maintained that its activities against Nicaragua were committed out of its desire to provide collective self-defense for El Salvador and other Central American states allegedly threatened by Nicaragua. The International Court of Justice (ICJ) heard the case and first decided that it did not have jurisdiction over Nicaragua’s claims based on Article 2(4) of the U.N. Charter. However, it did exercise jurisdiction over Nicaragua’s claims that the United States violated principles of customary international law. The United States defended its actions by arguing it was entitled to invoke the principle of “collective self-defense” in customary international law which permits such actions by a State on behalf of other States that have experienced an armed attack. The ICJ considered this argument. However, the Court held that the United States could not justify its military and paramilitary activities on the basis of collective self-defense. Customary international law allows for exceptions to the prohibition on the use of force – including the right to individual or collective self-defense. The United States, at an earlier stage of the proceedings, had asserted that the Charter itself acknowledges the existence of this customary international law right when it talks of the “inherent” right of a State under Article 51 of the Charter. On the other hand, when a State claims that it used force in collective self-defense, the Court would look into two aspects: whether the circumstances required for the exercise of self-defense existed and whether the steps taken by the State, which was acting in self-defense, corresponds to the requirements of international law (i.e. did it comply with the principles of necessity and proportionality). Several criteria must be met for a State to exercise the right of individual or collective self-defense: A State must have been the victim of an armed attack. Furthermore, this State must declare itself as a victim of an armed attack. In the case of collective self-defense – the victim State must request for assistance. The ICJ looked extensively into the conduct of Nicaragua, El Salvador, Costa Rica and Honduras in determining whether an armed attack was undertaken by Nicaragua against the three countries – which in turn would necessitate self-defense. The Court referred to statements made by El Salvador, Costa Rica, Honduras and the United States before the Security Council. None of the countries (who were allegedly subject to an armed attack by Nicaragua) declared themselves as a victim of an armed attack or request assistance from the United States in self-defense. As a result, the ICJ concluded that the United States cannot justify its use of force as collective self-defense. The United States breached its customary international law obligation – not to violate the sovereignty of another State – when it directed or authorized its aircrafts to fly over Nicaraguan territory and when it laid mines in the internal waters of Nicaragua and its territorial sea.