Pursuing War with Mexico
At the same time, with Texas now a state, Mexico faced growing tensions with the United States. Conflicts centered on Texas’s western border. Mexico insisted on the Nueces River as the boundary line, while Americans claimed all the land to the Rio Grande. In January 1846, Polk secretly sent emissary John Slidell to negotiate with Mexico, offering President José Herrera $30 million for New Mexico and California after securing the Rio Grande boundary. But Polk also sent U.S. troops under General Zachary Taylor across the Nueces River. Mexican officials refused to see Slidell and instead sent their own troops across the Rio Grande. Meanwhile U.S. naval commanders prepared to seize San Francisco Bay if war was declared. The Mexican government responded to these hostile overtures by sending more troops into the disputed Texas territory.
When fighting erupted near the Rio Grande in May 1846 (Map 10.3), Polk claimed that “American blood had been shed on American soil” and declared a state of war. Many Whigs in Congress protested, arguing that the president had provoked the conflict. Congressman Abraham Lincoln of Illinois demanded that Polk “show me the spot” where U.S. blood was shed. However, antiwar Whigs failed to convince the Democratic majority, and Congress voted to finance the war.
The South was solidly behind the war. As the Charleston, South Carolina, Courier declared: “Every battle fought in Mexico and every dollar spent there, but insures the acquisition of territory which must widen the field of Southern enterprise and power in the future.” Most Northerners also supported the war. Although ardent opponents of slavery protested, most Americans considered westward expansion a boon (see Map 10.3).
Once the war began, battles erupted in a variety of locations. In May 1846, U.S. troops defeated Mexican forces in Palo Alto and Resaca de la Palma. A month later, the U.S. army captured Sonoma, California, with the aid of local settlers. John Frémont then led U.S. forces to Monterey, California, where the navy launched a successful attack and declared the territory part of the United States. That fall, U.S. troops gained important victories at Monterrey, Mexico, just west of the Rio Grande, and Tampico, along the Gulf coast.
Although the Mexican army outnumbered U.S. forces, it failed to capitalize on this advantage. In the northern provinces, Mexican soldiers were ill equipped for major battles, and in the heart of Mexico divisions among political and military leaders limited battlefield success. Still, Mexican soldiers and residents fought fiercely against the American invaders.
Despite major U.S. victories, Santa Anna, who reclaimed the presidency of Mexico during the war, refused to give up. In February 1847, his troops attacked General Taylor’s forces at Buena Vista and nearly secured a victory. Polk then agreed to send General Winfield Scott to Veracruz with 14,000 soldiers. Capturing the port in March, Scott’s army marched on to Mexico City. After a crushing defeat of Santa Anna at Cerro Gordo, the president-general was removed from power, and the new Mexican government sought peace.
With victory ensured, U.S. officials faced a difficult decision: How much Mexican territory should they claim? The U.S. army in central Mexico faced continued guerrilla attacks. Meanwhile Whigs and some northern Democrats denounced the war as a southern conspiracy to expand slavery. In this context, Polk agreed to limit U.S. claims to the northern regions of Mexico. Eager to unite the Democratic Party before the fall election, the president signed the Treaty of Guadalupe Hidalgo in February 1848, and the U.S. Senate ratified it in March. The treaty committed the United States to pay Mexico $15 million in return for control over Texas north and east of the Rio Grande plus California and the New Mexico territory.