Throughout the 1820s, Americans settled in the vast
territory of Texas, often with land grants from the Mexican government.
Their numbers soon alarmed the authorities, however, who prohibited
further immigration in 1830. In 1834 General Antonio Lopez de Santa
Anna established a dictatorship in Mexico, and the following year Texans
revolted. Santa Anna defeated the American rebels at the celebrated
siege of the Alamo in early 1836, but Texans under Sam Houston destroyed
the Mexican army and captured Santa Anna a month later at the Battle
of San Jacinto, ensuring Texan independence. For almost a decade, Texas
remained an independent republic, becoming the 28th state in 1845.
Although Mexico broke relations with the United States
over the issue of Texas statehood, the most contentious
issue was the new state's border: Texas claimed the
Rio Grande River; Mexico argued that the border stood far to the north
along the Nueces River. Meanwhile, settlers were flooding into the territories
of New Mexico and California at a time when many Americans claimed that
the United States had a "manifest destiny" to expand westward to the
Pacific Ocean.
U.S. attempts to buy the New Mexico and California territories
failed, and after a clash of Mexican and U.S. troops along the Rio Grande,
the United States declared war in 1846. U.S. forces occupied the territory
of New Mexico, then supported the revolt of settlers in California.
A U.S. force under Zachary Taylor invaded Mexico, winning victories
at Monterey and Buena Vista, but failing to bring Mexico to the negotiating
table. In March 1847, U.S. forces commanded by Winfield Scott landed
near Vera Cruz on Mexico's east coast, and after a series of heavy engagements,
entered Mexico City. Nevertheless, it was only after the resignation
of Santa Anna that the United States was able to negotiate the Treaty
of Guadalupe Hildago in which Mexico ceded the Southwest region and
California for $15 million.
The war proved to be a training ground for American
officers who would later fight on both sides in the Civil War. It was
also a politically divisive war in which antislavery Whigs criticized
the Democratic administration of James K. Polk for expansionism.
With the conclusion of the Mexican War, the United States
gained a vast new territory of 1.36 million square kilometers encompassing
the present-day states of Arizona, Nevada, California, Utah and parts
of New Mexico, Colorado and Wyoming. But it was also a poisoned acquisition
because it revived the most explosive question in American politics
of the time: would the new territories be slave or free?