Larger in land mass than the contiguous United States, Brazil borders every country on the South American continent except Ecuador and Chile. Three features define Brazil's geography: the Amazon Basin, tropical savanna and the Brazilian Highlands. The Amazon River and rain forest, the world's largest, encompass most of northern Brazil and make this region inhospitable to agriculture and large populations. To its south lies the Cerrado, a vast tropical savanna. Advances in agricultural practices have allowed large-scale farming to thrive in this region. However, due to distance and geography, Brazil faces daunting challenges in getting agricultural commodities to international markets. The Brazilian Highlands and the narrow strip of land between the mountains and the coast are home to the majority of the country's 197 million people. Most of the country's economic activity occurs in this region. Brazil's geography largely shields it from external military threats. The Atlantic Ocean, the Amazon Basin and the buffer states of Bolivia, Paraguay and Uruguay insulate the country. Brazil's varied regions have made centralized control and integration difficult for the core states of Rio de Janeiro, Sao Paulo and Minas Gerais. Infrastructure linking the coast and the interior, as well as connecting the various coastal cities is technically difficult and requires high levels of investment. Isolated from the rest of the continent both geographically and linguistically and lacking internal cohesion, Brazil has traditionally been inward looking. Brazil's primary geographic challenging is consolidating control over its vast peripheral territory and connecting these regions more efficiently with its population centers and ports.