On 10 October 1986, Javier Pérez de Cuéllar of Peru again stood in front of the General Assembly to take the oath of office as Secretary-General of the United Nations:
"I solemnly swear to exercise in all loyalty, discretion and conscience the functions entrusted to me as Secretary-General of the United Nations; to discharge these functions and regulate my conduct with the interests of the United Nations only in view; and not to seek or accept instructions in regard to the performance of my duties from any Government or other authority external to the Organization."
A lawyer and career diplomat with the foreign ministry of Peru, Mr. Cuéllar held several high-level posts at the UN before becoming Secretary-General in 1982. His second term as the fifth Secretary-General ended in 1991.
In 1974, scientists published their first scientific hypotheses that chemicals produced by humans were harming the stratospheric ozone layer. The ozone layer protects the earth against excessive ultraviolet radiation, which can damage human, plant, and animal cells. Efforts of the United Nations Environment Programme led to the signing of a treaty designed to reduce the production and consumption of ozone depleting substances. The Treaty on the Protection of the Ozone Layer was adopted on 16 September 1987. The Montreal Protocol, as it is known, and its predecessor, the Vienna Convention for the Protection of the Ozone Layer are the first and only global environmental treaties with universal ratification. Secretary-General Ban Ki-moon stated in 2014, “Without the Protocol and associated agreements, atmospheric levels of ozone-depleting substances could have increased ten-fold by 2050. Concerted action has prevented millions of cases of skin cancer.”
On 6 December 1988, the UN General Assembly passes resolution 43/53, declaring climate change "a common concern of mankind” and establishing the Intergovernmental Panel on Climate Change (IPCC). The IPCC is tasked to prepare a comprehensive review of the scientific knowledge on climate change; to assess the social and economic impact of climate change, and to formulate response strategies. The first IPCC Assessment Report of 1990 underlined the importance of climate change as a challenge requiring international cooperation and played a role in the creation of the United Nations Framework Convention on Climate Change.
In 2007, the Intergovernmental Panel on Climate Change was awarded the Nobel Peace Prize for “efforts to build up and disseminate greater knowledge about man-made climate change and to lay the foundations for the measures that are needed to counteract such change."
On 9 November 1989, the Berlin Wall fell. Six days later, in a powerful symbol of the end of the cold war, the United States and the USSR jointly propose a political resolution for the first time in the history of the United Nations. Resolution 44/21 calls for a strengthening of the UN’s role in maintaining international peace and security.
Namibia's struggle for independence was on the United Nations agenda for over 40 years. The Security Council's landmark resolution 435(1978) had served as the pathway for independence for the last remaining colony in Africa. The UN Transition Assistance Group had monitored the electoral process and certified that they were free and fair, helping Namibia join the ranks of the community of nations. Secretary-General Javier Pérez de Cuéllar swore in the country’s first president.
“It is with great satisfaction that I have the honour to report to the Security Council that, shortly after midnight on 20/21 March 1990, at the National Stadium in Windhoek, the flag of the Republic of South Africa was lowered and the flag of the Republic of Namibia was raised, thus marking the accession of Namibia to independence,” writes Secretary-General Cuéllar in his final report on the implementation of resolution 435(1978).
The deployment of the United Nations Observer Mission El Salvador (ONUSAL) in 1991 was part of an expansion of UN peacekeeping in the early 1990’s. The cold war was over. With a new consensus and a common sense of purpose, the Security Council authorized a total of 20 new operations between 1989 and 1994, raising the number of peacekeepers from 11,000 to 75,000.
Peacekeeping operations in Asia, Europe, Central America, and Africa carried out ambitious missions. In El Salvador, for example, ONUSAL’s mandate was to verify implementation of all agreements between the Government of El Salvador and the Frente Farabundo Marti para la Liberacion Nacional, including a ceasefire and related measures, reform and reduction of the armed forces, creation of a new police force, reform of the judicial and electoral systems, human rights, land tenure and other economic and social issues.
On 31 January 1992, the first Security Council Summit, with leaders from all fifteen Security Council members in attendance, was held in New York. The meeting reaffirmed the central role of the Council in maintaining world peace and upholding the principle of collective security as envisioned in the UN Charter. At the summit, the Council invited Secretary-General Boutros Boutros-Ghali to prepare recommendations on ways to strengthen the UN's capacity in the areas of preventative diplomacy, peace-making, and peacekeeping.
In June, the Secretary-General presented “An Agenda for Peace" to the members of the UN. In addition to an analysis of the current peace and security framework employed by the UN, the Secretary-General added the new concept of post-conflict peace-building. Peace-building in the aftermath of conflict would be "action to identify and support structures which will tend to strengthen and solidify peace in order to avoid a relapse into conflict." He writes," These four areas for action, taken together, and carried out with the backing of all Members, offer a coherent contribution towards securing peace in the spirit of the Charter."
The late 1980s and early 1990s witnessed dramatic political and social change across eastern Europe and the Soviet Union with the collapse of the majority of communist systems and resurgence of nationalism. Following the violent break-up of Yugoslavia, reports of mass atrocities - massacres of thousands of civilians, rape and torture in detention camps, hundreds of thousands expelled from their homes - led the Security Council to decide it would establish an international tribunal for "prosecuting persons responsible for serious violation of international humanitarian law committee in the territory of the former Yugoslavia.”
On 25 May 1993, the Council passed resolution 827 formally establishing the International Criminal Tribunal for the former Yugoslavia (ICTY). The ICTY was the first war crimes court established by the UN and the first international war crimes tribunal since the Nuremberg and Tokyo tribunals. The following year, the UN created the International Criminal Tribunal for Rwanda to prosecute perpetrators of genocide in that country.
At the end of World War II, over a third of world’s population lived in dependant territories. The Trusteeship Council, one of the main organs of the United Nations, was established under Chapter XIII of the Charter to supervise the administration of Trust Territories and to ensure that Governments responsible for their administration took adequate steps to prepare them for the achievement of self-determination through independence or free association with an independent State.
In 1994, the Security Council terminated the United Nations Trusteeship Agreement for the last of the original 11 Territories on its agenda - the Trust Territory of the Pacific Islands (Palau), administered by the United States. With its historic mission completed, the Trusteeship Council voted to suspend operation and will now meet only as occasion requires.
On 24 October 1995, the largest gathering of world leaders ever assembled met to commemorate the fiftieth anniversary of the UN. The Declaration on the Occasion of the Fiftieth Anniversary of the United Nations, endorsed by the General Assembly, states:
"The United Nations has been tested by conflict, humanitarian crisis and turbulent change, yet it has survived and played an important role in preventing another global conflict and has achieved much for people all over the world. The United Nations has helped to shape the very structure of relations between nations in the modern age. Through the process of decolonization and the elimination of apartheid, hundreds of millions of human beings have been and are assured the exercise of the fundamental right of self-determination.
At this time, following the end of the cold war, and as the end of the century approaches, we must create new opportunities for peace, development, democracy and cooperation."