What country is south of the United States?

The country south of the United States is Mexico, officially the United Mexican States (Estados Unidos Mexicanos), bordered with the United States along the southern frontier of the four U.S. states of California, Arizona, New Mexico, and Texas, with the Rio Grande forming the boundary along Texas and a surveyed land border across the other three states. The U.S.-Mexico border runs about 1,954 miles total, the most-crossed international border in the world by volume of legal crossings. Mexico is the third largest country in North America after Canada and the United States, covering about 758,000 square miles, with a population of about 130 million in 2024, the tenth most populous country in the world. The capital is Mexico City, the largest metropolitan area in North America with about 22 million people. Mexico is a federal republic with 31 states plus Mexico City.

Spanish colonized the area beginning with Hernan Cortes' conquest of the Aztec Empire in 1519 to 1521, establishing the Viceroyalty of New Spain that lasted nearly 300 years. Mexico declared independence from Spain in 1810 and achieved it in 1821 after the Mexican War of Independence.

The current border with the United States resulted from a series of nineteenth century events. Texas seceded from Mexico in 1836 and joined the United States on December 29, 1845. The Mexican-American War from May 13, 1846 to February 2, 1848 ended with the Treaty of Guadalupe Hidalgo, in which Mexico ceded about 525,000 square miles including present-day California, Nevada, Utah, most of Arizona and New Mexico, and parts of Colorado and Wyoming for 15 million dollars. The Gadsden Purchase of December 30, 1853 added another 30,000 square miles for 10 million dollars.

Mexico and the United States have one of the most economically integrated relationships in the world. The North American Free Trade Agreement effective January 1, 1994 (replaced by the United States-Mexico-Canada Agreement effective July 1, 2020) has created a deeply linked North American market. Mexico is the United States' largest trading partner. About 11 million people of Mexican origin live in the United States, including about 4 million Mexican-born immigrants. Approximately 1.6 million American citizens live in Mexico. Cultural ties are extensive in language, food, music, and family relationships.

Issues like immigration, drug trafficking, and trade routinely shape U.S.-Mexico relations. The Pan-American Highway connects the two countries and continues south through Central and South America. Mexico is also a major Spanish-speaking country and a leading destination for American tourism, with sites including ancient Maya ruins, colonial cities, and Pacific and Caribbean beaches.