(Mar. 30, 2008) Other explanations for why the region has decided to pursue a strategy of South American unification focus on the cultural similarities between these nations. This interpretation emphasizes the post colonial Pan-American unification movement, begun by the early Liberators like Bolívar, Sucre, San Martin, or O'Higgins who said, “la patria de los americanos debía ser el continente entero.”  It also highlights the similarities of languages (Portugese and Castillian), a common Christian religion (Catholicism and Protestantism), legal philosophy, shared multiethnic cultures, etc. as examples of this inherent similarity. 
The identification of a regional union with the historic Pan-American movement has its most vocal supporters in governmental institutions who describe the current integration process in terms of an ongoing historic process begun two centuries earlier. This connection is made explicit in the preamble to the 2004 Declaration of Cuzco that states:
"We, the Presidents of the South American countries, gathered in the city of Cusco during the celebration of the heroic battles of Junín and Ayacucho and of the convening of the Amphictyonic Congress of Panama, following the example of the Liberator Simón Bolívar, of the Grand Marshal of Ayachuco, Antonio José de Sucre, of the Liberator José de San Martín, and of our pro-independence nations and heroes who built the great American Nation without any borders, interpreting the aspirations and hopes of their people for integration, unity and the construction of a common future, have decided to form the South American Community of Nations."
This expression of what we will call 'South American Manifest Destiny' is also visible in comments made by Eduardo Duhalde, former president of Argentina and Presidente de la Comission de representantes permanents del MERCOSUR, who said "[Unasur] is the dirección adoptada por la historia" or by Peruvian Ambassador Ernesto Pinto Bazurco who wrote that "la integración de América del Sur es un destino historic."   Finally, Allan Wagner, former Sec. Gen. Of the Comunidad Andina said "La integración es un proceso histórico. Todos nosotros somos de alguna manera actores circunstanciales de ese proceso." 
This theory of historical—cultural similarity is not universally accepted because it rests on the premise that the whole South American continent is so similar that it is seemingly preordained to unite. While it is true that the region does share a number of historical socio—economic problems (mercantilist colonial background; primary export economies; weak political institutions; ethnic tensions; income disparities; etc), the individual societies themselves are very different.
According to Fernando Moreno, "[América Latina] está…diversificada por la existencia de materias históricas específicas de naturaleza heterogénea, constituidas por grupos humanos étnica y culturalmente diferentes y por medios geográficos extremadamente variados según los países. 
The assumption of a common historical—cultural history of all of territorial South America as the basis for today's process is problematic because it does little to explain why previous attempts to unite were based on different criteria. The famous Bolivarian Pan—American Congress that met in Panama in 1826 was made up of delegates from the Hispano—American regions excluding the Lusophone and Anglophone countries. Finally, the 1960 Latin America Free Trade Agreement (LAFTA/ALALC) and its offspring the Latin American Integration Association (ALADI) of 1980 were both posited on a Latin American union open to Central America, the Caribbean States and South America. However, there is no reason to assume that UNASUR could not grow to encompass a more "traditional" Latin American membership.
By Nathan Gill - Southern Affairs
 Barros Van Buren, Mario. Historia Diplomática de Chile (1541-1938). 2nd. ed. 1958. Editorial Andrés Bello: Santiago de Chile 1990: 51  "The shared and unified history of our nations which, from the very heroic deeds in their striving for independence, have confronted common internal and external challenges, shows that our countries have a still untapped potential for making better use of their regional aptitudes and for reinforcing their capacities for international negotiation and projection;…" Declaration of Cusco, Dec. 8, 2004  El Comercio. Interview with Peruvian Ambassador Ernesto Pinto Bazurco. 27 Dec. 2004  Rafael Bielsa, former Argentinean Minister of Foreign Relations also called UNASUR the "unico porvenir común posible." Clarin de Argentina. "Nuestro destino sudamericano." Online 8 Dec. 2004  Rojas R., Ingrid. Interview with Allan Wagner Tizón Nos encontramos en la comunidad sudamericana. El Mundo de Venezuela: Caracas 31 May 2006.  Moreno, Fernando. 1978: 106-107
(Mar. 30, 2008) Other explanations for why the region has decided to pursue a strategy of South American unification focus on the cultural similarities between these nations. This interpretation emphasizes the post colonial Pan-American unification movement, begun by the early Liberators like Bolívar, Sucre, San Martin, or O'Higgins who said, “la patria de los americanos debía ser el continente entero.”  It also highlights the similarities of languages (Portugese and Castillian), a common Christian religion (Catholicism and Protestantism), legal philosophy, shared multiethnic cultures, etc. as examples of this inherent similarity.