Costa Rica was sparsely inhabited by indigenous people before it came under Spanish rule in the 16th century. Once a poor and isolated colony, since becoming independent in the 18th century, Costa Rica has become one of the most stable, prosperous, and progressive nations in Latin America. It constitutionally abolished its army permanently in 1949, becoming the first and one of the few sovereign nations without a standing army. A constitutional republic, it is the only Latin American country to have been a democracy since 1950 or earlier. Costa Rica has consistently been among the top-ranking Latin American countries in the Human Development Index. Indeed, in 2010 Costa Rica was cited by the United Nations Development Programme (UNDP) as having attained much higher human development than other countries at the same income levels, while in 2011, the UNDP also identified it as a good performer on environmental sustainability, with a better record on human development and inequality than the median of their region.