Central America's largest nation, Nicaragua, named after the powerful Indian chief Nicarao, currently has the region's lowest population density. Nicaragua attained independence in 1822 as part of the newly formed Mexican empire; the following year it joined the Central American Federation. Despite prolonged political and social turmoil, a segment of Nicaragua's population has always been devoted to learning and ideas. In 1906 Ruben Dario served as secretary to the Nicaraguan delegation to the Pan American Conference in Rio, where he tried to further inter-American cooperation. Augusto Sandino is as synonymous with Nicaragua's populist desire for liberation as Dario is with poetry. Carlos Fonseca Amador believed that only an educated populace could sustain a revolution, and he fostered the drive for education, reflected in the remarkable jump in books published in Nicaragua. Ernesto Cardenal returned to Nicaragua in 1966 and, on the poverty-stricken islands of Solentiname in the southern part of Lake Nicaragua, he founded a contemplative lay community.