U.S.-Mexican War

Texas annexation, however, caused a border dispute between Mexico and the United States. Texas claimed the Rio Grande as its southern boundary. Mexico insisted on the Nueces River as the border of Texas.

Border Dispute

President Polk ordered U.S. forces into the disputed area. To Mexican leaders, U.S. military action was an invasion of their country and Mexican troops attacked American forces in the disputed territory north of the Rio Grande.

President Polk Takes Action

President Polk told Congress "Mexico has invaded our territory and shed American blood upon American soil." He stated the U.S. needed to defend U.S. territory from Mexican aggression and stop Mexican attacks against U.S. territory. Congress passed a declaration of war against Mexico in what was known as the U.S.-Mexican War.

Congress Declares War

The war lasted from 1846-1848 and ended with American victories at the battles of Veracruz, Cerro Gordo and Mexico City (Mexico's capital). After Mexico's defeat in 1848, Mexican leaders signed the Treaty of Guadalupe Hidalgo to end the U.S.—Mexican War.

Mexico is Defeated

Mexican leaders signed the Treaty of Guadalupe Hidalgo to end the U.S.—Mexican War. With the treaty of Guadalupe Hidalgo the United States also acquired several territories from Mexico. Mexico ceded (gave) land to the United States, known as the Mexican Cession. Mexico also accepted the Rio Grande as its border with Texas. In return, the United States paid Mexico $15 million.

Mexican Cession

In 1850 a compromise was made which allowed much of the land gained from the U.S.-Mexican War to use popular sovereignty to determine whether the territory would be free or slave. Popular Sovereignty means the people living in the territory would vote to decide on the issue of slavery.

Compromise of 1850