At the Third South American Summit on 8 December 2004, presidents or representatives from 12 South American nations signed the Cusco Declaration, a two-page statement of intent announcing the foundation of the South American Community.
After Argentina, Bolivia, Chile, Ecuador, Guyana, Peru, Suriname and Venezuela, Uruguay became the ninth nation to ratify the constitutive treaty of the organization on 1 December 2010, thus completing the minimum number of ratifications Necessary for the entry into force of the Treaty, on 11 March 2011.
In August 2017, six members of UNASUR - Argentina, Brazil, Chile, Colombia, Paraguay and Peru - joined in forming the Lima Group, a coalition of Western Hemisphere nations that repudiates the Venezuela government of Nicolás Maduro as antidemocratic. In February 2018, Maduro was disinvited from the Summit of the Americas hosted by Peru (held in Lima in April 2018). In response, Bolivia's leftist president Evo Morales urged Unasur to defend Venezuela, stating "Unasur should call an emergency meeting and enforce the sovereignty of a brotherly people." <...>
On 20 April 2018, six countries - Argentina, Brazil, Chile, Colombia, Paraguay and Peru - announced that they would suspend their own membership for a year until the regional group became more organized.
In August 2018, Colombia announced its withdrawal from the organization.