The Mexican-American War (U.S. National Park Service) (2025)

On May 13, 1846, the United States declared war on Mexico, beginning the Mexican-American War. The Mexican-American War is one of the least known pivotal moments in US History. It paved the way for so many other important events, from the expansion and dispossession of indigenous people, the California Gold Rush, and American Civil War. It added the states of California, Texas, New Mexico, Utah, Arizona, Nevada, and parts of Colorado and Wyoming to the United States. American success in the war solidified belief in the concept of Manifest Destiny, confirming the idea that the United States had been destined by divine entities to expand into a continental empire resembling the present-day nation. For proponents of slavery and abolition, the new territory provided a source of conflict over whether slavery would expand and continue in the West. For the major military leaders of the Civil War on both the Confederate and Union sides, including such Pig War figures as Winfield Scott, George Pickett, and William Harney, it was a crucible in which their skills were tested, their tactics were formed, and they built the bonds of camaraderie that they relied on during the Civil War.

The immediate cause of the Mexican-American War was a disputed boundary between the United States and Texas on the Nueces Strip. Mexico did not recognize Texas as legitimate American territory and Texas admission to the United States antagonized Mexican officials and citizens. Rather than ameliorate this problem, President Polk intentionally worked to aggravate Mexico and provoke a war. On January 13, 1846, Polk ordered American forces into deeply disputed territory. In April, an army of approximately 4,000 men lead by General Zachary Taylor entered the Nueces Strip, a contested territory that Mexico and many Americans regarded as never having been a part of Texas. Polk knew this action would antagonize Mexican military forces stationed within sight of Taylor’s army at Matamoros. Colonel Hitchcock, who served with Zachary Taylor’s army, could see the real intention of his deployment from his vantage point on the front lines: “We have not one particle of right to be here. It looks as if the government sent a small force on purpose to bring on a war, so as to have a pretext for taking California and as much of this country as it chooses.”

On April 9, Taylor’s army deployed the bulk of its artillery within striking distance of the 16,000 person city of Matamoros, Mexico. The US Navy then cut Matamoros off from the Gulf of Mexico, creating a blockade by land and water of the Mexican civilians and soldiers just across the Nueces River from Taylor’s forces. On April 24, Mexican forces crossed the Matamoros River to break the blockade; Taylor sent a small force to respond, and the Mexican Army opened fire, killing 11 American soldiers. The site of this battlefield is now preserved as Palo Alto Battlefield National Historical Park.

When word reached Washington, D.C., two weeks later, President James K. Polk informed congress that: "The cup of forbearance had been exhausted even before the recent information from the frontier of the Del Norte [Rio Grande]. But now, after reiterated menaces, Mexico has passed the boundary of the United States, has invaded our territory and shed American blood upon the American soil. She has proclaimed that hostilities have commenced, and that the two nations are now at war.

Prior to these actions, America was deeply divided about the prospect of war with Mexico. Abraham Lincoln, then a US Congressman tried to challenge the war by demanding proof that the spot where the war began was on US soil. Transcendentalist Henry David Thoreau engaged in civil disobedience, going to jail because he refused to pay federal taxes that supported the war."

Most Americans, however rallied around the flag. Many individuals enlisted in the army, swelling the small US army with new recruits. These recruits were motivated by more than just patriotic feelings. As American forces rapidly defeated Mexican forces, sexual assaults, looting, and violence toward civilians and surrendered Mexican forces were common. At the highest level, Commanding General Winfield Scott forced Mexican authorities to pay massive ransoms that supported underfunded American troops in the field. Historian Amy Greenberg has also shown how racist attitudes that saw Mexicans as racial inferiors and anti-Catholic bigotry enabled American soldiers and leaders to justify extreme violence and what we would now regard as war crimes against Mexican forces and civilians.

The US military was wildly successful and used a combination of innovative strategy, competent officership, luck, and brutality to achieve victory. American forces captured Mexico City within 16 months of the war’s beginning and expeditionary forces also fought battles in California and New Mexico that enabled the seizure of vast tracts of territory. As the Mexican-American War came to an end, gold was discovered in California, causing a massive population surge on the West Coast that ensured continued American sovereignty over the entire West Coast and paved the way for the boundary conflict in the San Juan Islands.

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    The Mexican-American War (U.S. National Park Service) (2025)

    FAQs

    How did the Mexican-American War protect US national interests? ›

    Final answer: The Mexican American War significantly promoted the U.S. national interests, particularly through territorial expansion as in the Treaty of Guadalupe Hidalgo. This expansion aligned with the U.S.' concept of Manifest Destiny and led to both economical and population growth.

    What did the US do with the land from the Mexican-American War? ›

    Under the terms of the treaty negotiated by Trist, Mexico ceded to the United States Upper California and New Mexico. This was known as the Mexican Cession and included present-day Arizona and New Mexico and parts of Utah, Nevada, and Colorado (see Article V of the treaty).

    What caused the Civil War US National Park Service? ›

    What caused the Civil War? A number of issues ignited the Civil War: states' rights, the role of the federal government, the preservation of the Union, the economy; but all were inextricably bound to the institution of slavery.

    What were the three main causes of the Mexican-American War? ›

    The Mexican-American War of 1846-1848 was a combination of Mexican unwillingness to recognize Texas independence, the desire of Texans for statehood, and American desire for westward expansion.

    How did the Mexican-American War benefit the US? ›

    It paved the way for so many other important events, from the expansion and dispossession of indigenous people, the California Gold Rush, and American Civil War. It added the states of California, Texas, New Mexico, Utah, Arizona, Nevada, and parts of Colorado and Wyoming to the United States.

    Why was the US justified in the Mexican-American War? ›

    On May 9, 1846, Polk began to prepare a war message to Congress, justifying hostilities on the grounds of Mexican refusal to pay U.S. claims and refusal to negotiate with Slidell.

    What was the purpose of the National Park Service? ›

    Our Mission

    The National Park Service preserves unimpaired the natural and cultural resources and values of the National Park System for the enjoyment, education, and inspiration of this and future generations.

    Which two Civil War battlefields compromised the first national military park? ›

    COMMEMORATING CHICKAMAUGA AND CHATTANOOGA BATTLEFIELDS

    The effort to preserve the battlefields at Chickamauga and Chattanooga began more than ten years before Congress created the national military park.

    What problem was the National Park Service is created trying to fix? ›

    The goal of the Park Service created by the act was to "preserve, forever unimpaired, the sublime beauty, dignity, and nobility of national park landscapes;"3 the Organic Act was silent on issues of biological preservation as we would understand the term today.

    Why did Mexico lose the Mexican-American War? ›

    In his 1885 memoirs, former U.S. President Ulysses Grant (himself a veteran of the Mexican war) attributed Mexico's defeat to the poor quality of their army, writing: "The Mexican army of that day was hardly an organization.

    What sparked the Mexican-American War? ›

    One of the causes of this war were the continued claims to Texas from both the United States and Mexican governments. Other reasons were claims against the Mexican government by American citizens for damages during the continuous Mexican Revolutions of the period and the U.S. desire to claim California.

    What were 3 outcomes of the Mexican-American War? ›

    The United States received the disputed Texan 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.

    Why was the Mexican-American War significant to the United States quizlet? ›

    Mexico would lose almost half its territory to the U.S., including lands from Texas to California. The war was a key event in American History as it fulfilled its 'manifest destiny', encompassing land from the Atlantic Ocean to the Pacific.

    What extent did the Mexican War promote the national interest quizlet? ›

    To what extent did the Mexican War promote the national interest? The Mexican War did promote American expansion because the US fought Mexico for territory.

    What did US want from the Mexican-American War? ›

    Polk and others saw the acquisition of Texas, California, Oregon, and other territories as part of the nation's Manifest Destiny to spread democracy over the continent. The U.S. also tried to buy Texas and what was called “Mexican California” from Mexico, which was seen as an insult by Mexico, before war broke out.

    What did the Mexican-American War contribute? ›

    With the Treaty of Guadalupe Hidalgo, Mexico ceded over 525,000 square miles of territory to the United States in exchange for $15 million and the assumption of Mexican debts to American citizens, which reopened the slavery issue.

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