At the time Spain granted independence to Mexico in 1821, the land now comprising the state of Texas was very sparsely populated. The Mexican government actually encouraged the settlement of the area by American pioneers.

In 1823, Stephen Austin led 300 American families onto land granted to his father by the Mexican government. A prosperous province was greatly in the interest of Mexico, so no alarm was raised. Mexico was also interested in creating a buffer zone between the Mexican heartland and the Comanche tribe. There were, however, strings attached.

The American settlers were expected to become Mexican. All immigrants from the United States were by law forced to become Catholic. When the Mexican government outlawed slavery in 1829, it expected the Texans to follow suit. None of the conditions were met, and a great cultural war was underway.

In the hopes of easing tensions, Stephen Austin journeyed to Mexico City in 1833, but Mexico's dictator, Santa Anna, was not the negotiating type. Austin was simply thrown in jail. Although he was released after 18 months, relations between the Texans and the Mexicans deteriorated. Finally, in 1835 war broke out between Santa Anna's troops and a ragtag group of Texan revolutionaries. On March 2, 1836, representatives from Texas formally declared their independence. Four days later, Santa Anna completed an infamous siege on the Alamo mission.

Despite a 13-day holdout, the 187 Texans were crushed by Santa Anna's forces, which numbered 5,000 strong. The deaths of commander William Travis, Jim Bowie, and Davy Crockett angered Americans as cries of "Remember the Alamo!" rang throughout the land. Americans flocked to Texas, and, led by commander Sam Houston, defeated Santa Anna's forces. On May 14, 1836, Santa Anna grudgingly recognized Texan independence.

Most Texan-Americans wanted to be annexed by the United States. They feared that the Mexican government might soon try to recapture their land. Many had originally come from the American South and had great interest in becoming a Southern state. President Andrew Jackson saw trouble. Many Whigs and Abolitionists in the North refused to admit another slave state to the Union. Rather than risk tearing the nation apart over this controversial issue, Jackson did not pursue annexation. The Lone Star flag flew proudly over the Lone Star Republic for nine years.

While Polk awaited the Presidency, the trouble of Texas resurfaced. Congress admitted Texas to the Union in a joint resolution passed the day before Polk's inauguration. Mexico was outraged. Inclusion in the United States would forever rule out the possibility of re-acquiring the lost province. Furthermore, the boundary was in dispute. Mexico claimed that the southern boundary of Texas was the Nueces River, the Texan boundary while under Mexican rule. Americans, as well as the incoming president, claimed that the boundary of Texas was the Rio Grande River. The territory between the two rivers was the subject of angry bickering between the two nations. Soon it would serve as the catalyst for an all-out war.

President Polk's true goal was to acquire the rich ports of California. He envisioned a lucrative trade with the Far East that would revolve around San Francisco and Monterey. Great Britain also had designs on the territory, so Polk thought he would have to act fast. He sent John Slidell to Mexico with an offer. The United States would pay Mexico a combined sum of $30 million for the Texan boundary of the Rio Grande, New Mexico Territory, and California.

The Mexican government was livid. They were not interested in selling the valuable territory. Instead, they issued the highest diplomatic rebuke. They refused even to receive Slidell to hear his offer. The American president was enraged. He resolved to fight Mexico.

In July of 1845, Polk ordered General Zachary Taylor to cross the Nueces River with his command of 4,000 troops. Upon learning of Slidell's rejection, Polk sent word that Taylor should advance his troops to the Rio Grande River. From the standpoint of Mexico, the United States had invaded their territory. Polk hoped to defend the disputed area with armed force. He also knew that any attack on American troops might provide what Congress was lacking to declare war.

Sure enough, in May of 1846, Polk received word that the Mexican army had indeed fired on Taylor's soldiers. Polk appeared before Congress on May 11 and declared that Mexico had invaded the United States and had "shed American blood on American soil!" Anti-expansionist Whigs had been hoping to avoid conflict, but news of the "attack" was too much to overlook. Congress passed a war declaration by an overwhelming majority. President Polk had his war.

Polk directed the war from Washington, D.C. He sent a four-prong attack into the Mexican heartland. John Fremont and Stephen Kearny were sent to control the coveted lands of California and New Mexico. Fremont led a group of zealous Californians to declare independence even before word of hostilities reached the West. The "Bear Flag Republic" was not taken seriously, but Fremont and his followers did march to Monterey to capture the Mexican presidio, or fort. By 1847, California was secure. Meanwhile, Kearny led his troops into Santa Fe in August of 1846, causing the governor of New Mexico to flee. The city was captured without a single casualty. Soon he marched his army westward across the desert to join Fremont in California.

The attack on Mexico proper was left to two other commanders: Zachary Taylor crossed the Rio Grande with his troops upon Polk's order. He fought Santa Anna's troops successfully on his advance toward the heart of Mexico. Winfield Scott delivered the knockout punch. After invading Mexico at Vera Cruz, Scott's troops marched to the capital, Mexico City. All that remained was negotiating the terms of peace.

The Mexican-American War was formally concluded by the Treaty of Guadalupe-Hidalgo. The United States received the disputed Texas Territory, as well as New Mexico Territory, and California. The Mexican government was paid $15 million--the same sum issued to France for the Louisiana Territory. The United States Army won a grand victory. Although suffering 13,000 men, the military won every engagement of the war. Mexico was stripped of half of its territory and was not consoled by the monetary settlement.