Pan Am Flight 103 was a regularly scheduled Pan Am transatlantic flight from Frankfurt to Detroit via a stopover in London and another in New York City. The transatlantic leg of the route was operated by Clipper Maid of the Seas, a Boeing 747-121 registered N739PA. Shortly after 19:00 on 21 December 1988, while the aircraft was in flight over the Scottish town of Lockerbie, it was destroyed by a bomb that had been planted on board, killing all 243 passengers and 16 crew in what became known as the Lockerbie bombing. Large sections of the aircraft crashed in a residential street in Lockerbie, killing 11 residents. With a total of 270 fatalities, it is the deadliest terrorist attack in the history of the United Kingdom, as well as its deadliest aviation disaster.Following a three-year joint investigation by Dumfries and Galloway Constabulary and the US Federal Bureau of Investigation (FBI), arrest warrants were issued for two Libyan nationals in November 1991. In 1999, Libyan leader Muammar Gaddafi handed over the two men for trial at Camp Zeist, the Netherlands, after protracted negotiations and UN sanctions. In 2001, Abdelbaset al-Megrahi, a Libyan intelligence officer, was jailed for life after being found guilty of 270 counts of murder in connection with the bombing. In August 2009, he was released by the Scottish government on compassionate grounds after being diagnosed with prostate cancer. He died in May 2012 as the only person to be convicted for the attack.

In 2003, Gaddafi accepted responsibility for the Lockerbie bombing and paid compensation to the families of the victims, although he maintained that he had never given the order for the attack. Acceptance of responsibility was part of a series of requirements laid out by a UN resolution for sanctions against Libya to be lifted. Libya said it had to accept responsibility due to Megrahi's status as a government employee.During the First Libyan Civil War in 2011, former Minister of Justice Mustafa Abdul Jalil claimed that the Libyan leader had personally ordered the bombing, though this was later denied, while investigators have long believed that Megrahi did not act alone, and have been reported as questioning retired Stasi agents about a possible role in the attack.

Some relatives of the dead, including Lockerbie campaigner Jim Swire, believe the bomb was planted at Heathrow Airport, and not sent via feeder flights from Malta, as the US and UK claim. A sleeper cell belonging to the Popular Front for the Liberation of Palestine (General Command) had been operating in West Germany in the months before the Pan Am bombing.On the 32nd anniversary of the bombing, 21 December 2020, Abu Agila Mohammad Masud was charged in the US for having built the bomb that destroyed the aircraft and acting as a co-conspirator.

The United Nations Organization (UNO) or just United Nations (UN) is an intergovernmental organization whose purpose is to maintain international peace and security, develop friendly relations among nations, achieve international cooperation, and be a centre for harmonizing the actions of nations. It is the world's largest and most familiar international organization. The UN is headquartered on international territory in New York City, and has other main offices in Geneva, Nairobi, Vienna, and The Hague (home to the International Court of Justice).

The UN was established after World War II with the aim of preventing future wars, succeeding the rather ineffective League of Nations. On 25 April 1945, 50 governments met in San Francisco for a conference and started drafting the UN Charter, which was adopted on 25 June 1945 and took effect on 24 October 1945, when the UN began operations. Pursuant to the Charter, the organization's objectives include maintaining international peace and security, protecting human rights, delivering humanitarian aid, promoting sustainable development, and upholding international law. At its founding, the UN had 51 member states; with the addition of South Sudan in 2011, membership is now 193, representing almost all of the world's sovereign states.The organization's mission to preserve world peace was complicated in its early decades by the Cold War between the United States and Soviet Union and their respective allies. Its missions have consisted primarily of unarmed military observers and lightly armed troops with primarily monitoring, reporting and confidence-building roles. UN membership grew significantly following widespread decolonization beginning in the 1960s. Since then, 80 former colonies have gained independence, including 11 trust territories that had been monitored by the Trusteeship Council. By the 1970s, the UN's budget for economic and social development programmes far outstripped its spending on peacekeeping. After the end of the Cold War, the UN shifted and expanded its field operations, undertaking a wide variety of complex tasks.The UN has six principal organs: the General Assembly; the Security Council; the Economic and Social Council (ECOSOC); the Trusteeship Council; the International Court of Justice; and the UN Secretariat. The UN System includes a multitude of specialized agencies, funds and programmes such as the World Bank Group, the World Health Organization, the World Food Programme, UNESCO, and UNICEF. Additionally, non-governmental organizations may be granted consultative status with ECOSOC and other agencies to participate in the UN's work.

The UN's chief administrative officer is the secretary-general, currently Portuguese politician and diplomat António Guterres, who began his first five year-term on 1 January 2017 and was re-elected on 8 June 2021. The organization is financed by assessed and voluntary contributions from its member states.

The UN, its officers, and its agencies have won many Nobel Peace Prizes, though other evaluations of its effectiveness have been mixed. Some commentators believe the organization to be an important force for peace and human development, while others have called it ineffective, biased, or corrupt.