Mexico is bordered by the United States to the north and Belize and Guatemala to the southeast. Mexico is about one-fifth the size of the United States. Baja California in the west is an 800-mile (1,287-km) peninsula that forms the Gulf of California. In the east are the Gulf of Mexico and the Bay of Campeche, which is formed by Mexico's other peninsula, the Yucatán. The center of Mexico is a great, high plateau, open to the north, with mountain chains on the east and west and with ocean-front lowlands beyond.
At least three great civilizations—the Mayas, the Olmecs, and the Toltecs—preceded the wealthy Aztec empire, conquered in 1519–1521 by the Spanish under Hernando Cortés. Spain ruled Mexico as part of the viceroyalty of New Spain for the next 300 years until Sept. 16, 1810, when the Mexicans first revolted. They won independence in 1821.
From 1821 to 1877, there were two emperors, several dictators, and enough presidents and provisional executives to make a new government on the average of every nine months. Mexico lost Texas (1836), and after defeat in the war with the U.S. (1846–1848), it lost the area that is now California, Nevada, and Utah, most of Arizona and New Mexico, and parts of Wyoming and Colorado under the Treaty of Guadalupe Hidalgo.
In 1855, the Indian patriot Benito Juárez began a series of reforms, including the disestablishment of the Catholic Church, which owned vast property. The subsequent civil war was interrupted by the French invasion of Mexico (1861) and the crowning of Maximilian of Austria as emperor (1864). He was overthrown and executed by forces under Juárez who again became president in 1867.