The Union of South American Nations (USAN; Spanish: Unión de Naciones Suramericanas, UNASUR; Portuguese: União de Nações Sul-Americanas, UNASUL; Dutch: Unie van Zuid-Amerikaanse Naties, UZAN; and sometimes referred to as the South American Union) is an intergovernmental regional organization that once comprised twelve South American countries; as of 2019, most have withdrawn.
The UNASUR Constitutive Treaty was signed on 23 May 2008, at the Third Summit of Heads of State, held in Brasília, Brazil. According to the Constitutive Treaty, the Union's headquarters will be located in Quito, Ecuador. On 1 December 2010, Uruguay became the ninth state to ratify the UNASUR treaty, thus giving the union full legality. As the Constitutive Treaty entered into force on 11 March 2011, UNASUR became a legal entity during a meeting of Foreign Ministers in Mitad del Mundo, Ecuador, where they had laid the foundation stone for the Secretariat Headquarters.
In April 2018, six countries - Argentina, Brazil, Chile, Colombia, Paraguay and Peru - suspended their membership, and in August of the same year, Colombia announced its withdrawal from the organization. In March 2019, Brazil's president Jair Bolsonaro announced his country's intention to withdraw from the organization. On March 13, 2019, Ecuador announced that it will withdraw from the organization. The president of the country, Lenin Moreno, also asked the bloc to return the headquarters building of the organization, based in Quito.