Why did the Mexican government encourage Americans to settle in Texas? Why did it begin to regret encouraging them to do so?

In the 1840s, the United States added greatly to its territory, gaining lands stretching all the way to the Pacific Ocean. President James K. Polk, who was elected on 1844 on the pledge to annex vast territories in the West, delivered on his major campaign promise.

In 1845, after a decade of controversy with Mexico, the state of Texas joined the U.S. After defeating Mexico in a war between 1846 and 1848, the U.S. acquired land in present-day Texas, New Mexico, Arizona, California, Nevada, and Utah. At the same time, the U.S. also gained possession of present-day Oregon and Washington from Canada.

Not all Americans favored westward expansion. As a result, the Mexican-American War proved extremely controversial. Many opponents of slavery feared that one of the chief goals of westward expansion was to acquire land into which slavery could spread. Indeed, westward expansion, and repeated arguments over whether the new territories and states in the West would permit or prohibit slavery, became one of the main disputes that led to the Civil War in the 1860s.

The United States was not the only nation in the Western hemisphere that declared itself independent in the late 18th and early nineteenth century. Many South American nations also declared themselves independent from European empires. In 1821, Mexico gained its independence from Spain.

The newly independent nation of Mexico extended far to the north of its current boundary, and included much of the land that Americans today consider the Southwest. (To Mexicans, this land was known as el Norte, "the North.") In the 1820s, Northern Mexico had relatively few settlers. The north was Mexico's frontier, lying hundreds of miles north of the capital in Mexico City. Because the Mexican government was eager to see this land occupied, it encouraged settlers, including U.S. citizens, to move there. By 1835, about 30,000 Americans, most of them from the Southern states, moved westward into eastern Texas. These American migrants brought with them approximately 5,000 slaves. Bringing slaves into Mexico provoked controversy, because slavery was outlawed in Mexico in 1829. As a result, white slave holders and the Mexican government soon came into conflict.

Because Texas lay far to the north of the center of the Mexican population and capital, the Mexican government had difficulty controlling it. Texans declared themselves an independent nation in March 1836, but Mexico attempted to stop the Texans' rebellion. In March, in a battle at the Alamo in San Antonio, Mexican forces under General Antonio Lopez de Santa Anna defeated the Texans, killing all 187 men defending the Alamo. The most famous casualty of this battle was frontiersman and politician Davy Crockett. "Remember the Alamo!" became a rallying cry for Texans in their war for independence.

The following year, Texans commanded by Sam Houston defeated Santa Anna's army, winning their independence. The Mexican government signed a treaty recognizing Texas's independence, but soon repudiated this treaty. Texas existed as an independent nation from 1836 to 1845. The Mexican government refused to recognize the legitimacy of the Texas government, insisting that Texans had no right to rebel against Mexico. Controversy between Texas, Mexico, and the U.S. festered in the 1840s.