Under the charter, the members of the UN vest in the Security Council primary responsibility for maintaining international peace and security. To facilitate its work and to ensure quick and effective action when required, the council has certain powers and attributes not accorded the other organs of the UN. Thus, the council is empowered by the charter to enforce its decisions and prescribe them as a course of action legally binding upon all UN members. However, these prerogatives can be invoked only in times of gravest crisis and under explicit conditions laid down in the charter. Otherwise, the Security Council, like the General Assembly, can only recommend and advise.
Another distinctive feature of the council is the membership and voting privileges accorded to the five countries that were chiefly responsible for the defeat of the Axis nations in World War II and, at the time of the San Francisco Conference, were regarded as militarily the most powerful countries in the world. By the terms of these privileges, China, France, the USSR, the United Kingdom, and the United States were each accorded permanent membership on the Security Council and the right to veto any substantive decision adopted by the majority of the other members. The underlying consideration here was the desire to preserve the unanimity of the Big Five—that is, to ensure that no peacekeeping action would be taken against the will of a country considered sufficiently powerful to oppose the council's decision with military force and so open up the possibility of a third major international war.
Since all five countries were actually specified by name in the relevant charter provisions, an amendment or revision of the charter would be required to name different nations as permanent Security Council members. In turn, a charter amendment requires ratification by all five permanent members of the Security Council before it can come into force. In 1971, a major change was brought about without altering the names of permanent members. The General Assembly voted that the right to represent China belonged to a delegation that the People's Republic of China would name and expelled the delegation from the Republic of China (Taiwan). On 24 December 1991, Boris Yeltsin, president of the new Russian Federation, sent a letter to the Secretary-General informing him that the Russian Federation, as the "continuing state" of the former USSR, would occupy the seat of the former USSR on the Security Council. The letter stated that the Russian Federation had the support of the 11 member countries of the Commonwealth of Independent States, most of whom subsequently became members of the United Nations. The precedent for this switch was cited as the 1947 accession of the newly independent India to the UN membership held by the former British India.