United Nations troops recapture Seoul from North Korean forces.

Seoul (; Korean: [sul] (listen); lit.'Capital'), officially known as the Seoul Special City, is the capital and largest metropolis of South Korea. According to the 2020 census, Seoul has a population of 9.9 million people, and forms the heart of the Seoul Capital Area with the surrounding Incheon metropolis and Gyeonggi province. Considered to be a global city and rated as an Alpha City by Globalization and World Cities Research Network (GaWC), Seoul was the world's 4th largest metropolitan economy in 2014 after Tokyo, New York City and Los Angeles.

Seoul was rated Asia's most livable city with the second highest quality of life globally by Arcadis in 2015, with a GDP per capita (PPP) of around $40,000. With major technology hubs centered in Gangnam and Digital Media City, the Seoul Capital Area is home to the headquarters of 15 Fortune Global 500 companies, including Samsung, LG, and Hyundai. Ranked seventh in the Global Power City Index and Global Financial Centres Index, the metropolis exerts a major influence in global affairs as one of the five leading hosts of global conferences. Seoul has hosted the 1986 Asian Games, 1988 Summer Olympics, and the 2010 G20 Seoul summit.

Seoul was the capital of various Korean states, including Baekje, Joseon, the Korean Empire, Goryeo (as a secondary capital), and presently South Korea. It is strategically located along the Han River. Seoul's history stretches back over two thousand years, when it was founded in 18 BC by the people of Baekje, one of the Three Kingdoms of Korea. The city was later designated the capital of Korea under the Joseon dynasty. Seoul is surrounded by a mountainous and hilly landscape, with Bukhan Mountain located on the northern edge of the city. The Seoul Capital Area contains five UNESCO World Heritage Sites: Changdeok Palace, Hwaseong Fortress, Jongmyo Shrine, Namhansanseong and the Royal Tombs of the Joseon Dynasty. More recently, Seoul has been a major site of modern architectural construction major modern landmarks include the N Seoul Tower, the 63 Building, the Lotte World Tower, the Dongdaemun Design Plaza, Lotte World, Trade Tower, COEX, and the IFC Seoul. Seoul was named the 2010 World Design Capital. It is the birthplace of K-pop and the Korean wave.

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.