The Mexican-American War began in 1846. The United States had annexed Texas the year before, but Mexico still claimed Texas as its own. The two countries also disagreed about where the border should be. Mexico claimed it was at the Nueces River, while the United States stated it was farther south, at the Rio Grande. President James K. Polk wanted more land for the nation, including California, but Mexico refused to sell. Polk sent American troops into the disputed area. When Mexican and American soldiers clashed, Polk asked Congress for war. On May 13, 1846, the United States declared war on Mexico.
Fighting broke out in several places. General Zachary Taylor led U.S. soldiers near the Rio Grande. Although the Mexican army was larger, Taylor’s troops won the first battles at Palo Alto and Resaca de la Palma. Farther west, Colonel Stephen W. Kearny marched into New Mexico and California. In many places, American soldiers and settlers faced little resistance. Another army under General Winfield Scott carried out a risky attack on Mexico’s east coast. In March 1847, his troops landed at the port of Veracruz. From there, they marched inland, winning battles at Cerro Gordo, Contreras, and Churubusco. In September 1847, U.S. forces entered Mexico City. With its capital taken, Mexico could no longer fight.
The war ended with the Treaty of Guadalupe Hidalgo, signed on February 2, 1848. The treaty set the Rio Grande as the border of Texas. Mexico also ceded a vast area of land to the United States, known as the Mexican Cession. This included California and New Mexico, as well as parts of today’s Arizona, Nevada, Utah, Colorado, and Wyoming. In return, the United States paid Mexico $15 million and agreed to settle some debts owed to U.S. citizens. The treaty allowed the United States to reach from the Atlantic Ocean to the Pacific Ocean.
Winning the war made the United States much larger, but it also created new arguments. People in the North and South disagreed about whether slavery should spread into the new lands. These arguments grew stronger in the years ahead and pushed the country closer to civil war.
