The status of Texas was in limbo—the United States government was undecided whether or not to grant the Republic statehood. To complicate matters, Mexico never formally recognized Texas’ independence. The Mexican government simply viewed Texas as a rebellious territory that they would eventually reconquer.
Meanwhile, President James Polk looked farther west for areas to expand the young nation. In 1845, Polk sent a diplomat to Mexico with an offer to purchase New Mexico and California from the Mexican government. He also wanted Mexico to agree to establish the Rio Grande river as the border between the two countries, which would make Texas part of the United States. As payment, the United States would relinquish legal claims against Mexico, an amount totaling more than $3 million.
The people of Mexico were still angered by the issue of Texas’ independence, however, and public sentiment forced the Mexican government to refuse any deal with the United States. The Mexican government still considered Texas part of their republic. Polk was outraged, and sent military forces, under the direction of Zachary Taylor, to the Rio Grande river. Skirmishes immediately broke out. One of these battles took place just north of the Rio Grande, in disputed territory. Polk interpreted this as an act of aggression against the United States and asked Congress to declare war on Mexico, which it did.
During this time, Taylor’s army was winning battles with regularity in the Rio Grande area. Taylor pushed into Northern Mexico while to the west Americans were infiltrating northern California. Soon, a rebellion against Mexican rule in California was underway. By mid-1846, California was known as the Bear-Flag Republic, which had a brief life span of 19 days. The U.S. military occupied the Los Angeles area and declared authority over the whole republic. Control of California was the heart of Polk’s Manifest Destiny doctrine, the belief that providence had willed the Americans a moral mission to conquer adjacent lands.
Although victory in California and New Mexico had been gained with relative ease, there were a few battles of note, including the Battle of San Pasqual, the only one in which the Americans were defeated by the Californios, people of Spanish, Indian and Mexican blood who ruled California before the American takeover.
On Dec. 6, 1846, Mexican troops under the command of Major Andrés Pico encountered U.S. forces -- led by Brigadier General Stephen W. Kearny -- at San Pasqual, in the northeastern area of what is now the County of San Diego in Southern California. The Californios inflicted heavy casualties on the Americans, who, having lost the battle, retreated to San Diego. The Americans would later defeat Pico’s forces in several battles throughout the state and Pico eventually surrendered in January, 1847, signing the Cahuenga Capitulaton that ended hostilities in California.
In New Mexico, Gov. Bent and others sympathetic to the American takeover were killed on Jan. 19, 1847 by a group of Spanish descendants, Indians and Mexicans. It was the start of what became known as the Taos Revolt. The New Mexicans were opposed to the occupation of their territory by U.S. forces. Col. Sterling Price and his troops retaliated, defeating the rebels at Santa Cruz, and later at Taos, where Price’s forces decisively beat the insurgents in a final battle that took place at the Taos Pueblo Church.
Feeling secure with California and New Mexico under U.S. control, Polk sent peace offerings to Mexico, which continually failed. Polk continued his effort at peace, however, and asked Congress for $2 million to buy the cherished western lands of New Mexico and California and end the war. The Senate agreed, but the House denied the motion. Their denial was largely due to the Wilmot Proviso that was added to the motion. In the Wilmot Proviso, Polk attempted to have Congress mandate that no slavery would be allowed in any territory acquired as a product of the Mexican War.
Discouraged, Polk started on another strategy to end the war. No significant progress was made in peace accords, however, until the Army seized Mexico City. Shortly after the New Year of 1848, the peace Treaty of Guadalupe-Hidalgo was completed and the war ended.
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