Brazil, officially the Federative Republic of Brazil, is the largest country in both South America. Brazil is the world's fifth-largest country by area and the sixth most populous.Its capital is Brasília, and its most populous city is São Paulo. The federation is composed of the union of the 26 states and the Federal District. It is the largest country to have Portuguese as an official language and the only one in the Americas. It is also one of the most multicultural and ethnically diverse nations, due to over a century of mass immigration from around the world. It borders all other countries in South America except Ecuador and Chile. Its Amazon River basin includes a vast tropical forest, home to diverse wildlife, a variety of ecological systems, and extensive natural resources spanning numerous protected habitats. Brazil's current constitution, formulated in 1988, defines it as a democratic federal republic.