Mexico (Spanish: México, pronounced: [ˈme.xi.ko] ), officially the United Mexican States (Spanish: Estados Unidos Mexicanos, ), is a country in the southern half of North America. It is bordered to the north by the United States; to the south and west by the Pacific Ocean; to the southeast by Guatemala, Belize, and the Caribbean Sea; and to the east by the Gulf of Mexico. Covering almost two million square kilometers (over 760,000 sq mi), Mexico is the sixth largest country in the Americas by total area and the 13th largest independent nation in the world. With an estimated population of over 120 million, it is the eleventh most populous country and the most populous Spanish-speaking country in the world while being the second most populous country in Latin America. Mexico is a federation comprising thirty-one states and a Federal District, its capital and largest city. Pre-Columbian Mexico was home to many advanced Mesoamerican civilizations, such as the Olmec, Toltec, Teotihuacan, Zapotec, Maya and Aztec before first contact with Europeans. In 1521, the Spanish Empire conquered and colonized the territory from its base in Mexico-Tenochtitlan, which was administered as the Viceroyalty of New Spain. Three centuries later, this territory became Mexico following recognition in 1821 after the colony's Mexican War of Independence. The tumultuous post-independence period was characterized by economic instability and many political changes. The Mexican–American War (1846–48) led to the territorial cession of the extensive northern borderlands, one-third of its territory, to the United States. The Pastry War, the Franco-Mexican War, a civil war, two empires and a domestic dictatorship occurred through the 19th century. The dictatorship was overthrown in the Mexican Revolution of 1910, which culminated with the promulgation of the 1917 Constitution and the emergence of the country's current political system. Mexico has the fifteenth largest nominal GDP and the eleventh largest by purchasing power parity. The Mexican economy is strongly linked to those of its North American Free Trade Agreement (NAFTA) partners, especially the United States. Mexico was the first Latin American member of the Organisation for Economic Co-operation and Development (OECD), joining in 1994. It is classified as an upper-middle income country by the World Bank and a newly industrialized country by several analysts. By 2050, Mexico could become the world's fifth or seventh largest economy. The country is considered both a regional power and middle power, and is often identified as an emerging global power. Due to its rich culture and history, Mexico ranks first in the Americas and sixth in the world by number of UNESCO World Heritage Sites. In 2015 it was the 9th most visited country in the world, with 32.1 million international arrivals. Mexico is a member of the United Nations, the World Trade Organization, the G8+5, the G20, the Uniting for Consensus and is an observer of the Organisation internationale de la Francophonie since 2014.