Mexican–American War

The Mexican–American War lasted from April 25, 1846, to February 2, 1848. It began when the United States invaded Mexico after taking over Texas in 1845. Mexico still thought Texas was its own land because it did not recognize the Treaties of Velasco signed by President Antonio López de Santa Anna. The Republic of Texas had been its own country, but many people there wanted to join the United States.

The war started after U.S. President James K. Polk sent soldiers into an area that both countries argued over. Mexican forces fought back, and this led the U.S. Congress to declare war. U.S. forces moved quickly and took control of places like Santa Fe de Nuevo México and Alta California. Finally, U.S. troops entered Mexico City in 1847.

The war ended with the Treaty of Guadalupe Hidalgo in 1848. Mexico gave up large parts of its land, including parts of today’s Texas, California, Nevada, Utah, and other states. In return, the United States paid Mexico $15 million and agreed to take on some of Mexico’s debt to American citizens. This war caused many debates in the United States and added to tensions that later helped cause the American Civil War.

Background

Mexico after independence from Spain

Mexico became free from Spain in 1821 after a long fight. The war hurt Mexico's main money-maker—silver mining—and left the country with many problems. Even though Mexico had trouble controlling some areas, it still tried to protect its land.

U.S. expansionism

Main article: Manifest destiny

In the early 1800s, the United States grew and wanted more land. After buying a large area called the Louisiana Purchase in 1803, the U.S. wanted to settle questions about its borders. The U.S. also wanted to buy land from Mexico to help its economy, especially because people wanted more cotton. Many Americans believed it was their right to expand westward.

Instability in northern Mexico

Mexico's northern areas were hard to control after independence. Attacks from Native American tribes like the Comanche and Apache made life difficult for people living there. The Mexican government was busy with its own problems and could not protect these areas well. This made it easier for the U.S. to later move into the region.

Foreign designs on California

Some leaders from other countries, like the United States and Britain, wanted California's rich land. They thought Mexico might sell or share control of California. However, Mexico still considered it their own, and there were tensions over who should control the area.

Texas revolution, republic, and U.S. annexation

Main articles: Texas Revolution, Republic of Texas, and Texas annexation

In the early 1800s, many American families moved to Texas, which was part of Mexico. Over time, these settlers wanted more control and declared independence from Mexico in 1836. After battles, Texas became its own country. In 1845, Texas agreed to join the United States, becoming the 28th state. This made Mexico very upset and led to conflicts between the two nations.

Prelude

Nueces Strip

After Texas became independent from Mexico, the southern border of Texas was set at the Rio Grande River. Texans thought this meant the border was at today’s Rio Grande. But Mexico disagreed. They said the border should be at the Nueces River instead. They argued that Texas was not truly independent and that the Rio Grande in the treaty was actually the Nueces River.

Polk's actions

In 1845, President Polk sent General Zachary Taylor to Texas with troops. They were placed near the Nueces River, ready to claim the disputed land. Polk also talked to leaders in California, offering support for independence from Mexico. But he warned them not to let European countries take control. To avoid a conflict with Britain over Oregon, Polk agreed to split the Oregon Country between the two nations. This upset some people in the North who wanted more land for the U.S.

Mexico's response

Mexico was unstable at this time, with leaders changing often. Mexicans strongly felt that selling land to the United States would dishonor their country. Those who suggested peace talks were seen as traitors. When President Herrera thought about talking to the U.S. representative, he was removed from power. The new government firmly said that Texas still belonged to Mexico.

Preparation for war

Challenges in Mexico

The Mexican Army had many problems. Only a few states sent soldiers, money, and weapons. Leaders like Santa Anna tried to train volunteers, but it was hard to make them work together.

Mexican forces were split into two groups: permanent soldiers and local militia. In the north, special groups protected towns. Indigenous people helped defend their land. They sometimes joined the Mexican Army but were not always treated well.

Mexican soldiers used older British muskets from the Napoleonic Wars. American soldiers used better rifles and revolvers, and they had stronger artillery.

There were also political problems in Mexico. Different groups fought for control, and presidents changed often. This made it hard to organize a strong defense.

Challenges in the United States

The U.S. Army was smaller and needed help from volunteer regiments from different states. Some volunteers were not well-trained. The U.S. Navy also sent sailors to fight in California.

The U.S. Army started with eight infantry regiments, four artillery regiments, and three mounted regiments. Congress added ten more regiments in 1847. Many soldiers were recent immigrants. Some volunteers only wanted to stay for a short time. They faced disease and hard conditions.

Political divisions in the U.S. grew because of the war, especially over slavery. President Polk’s Democrats lost control of the House of Representatives to the Whig Party, which opposed the war. However, the U.S. managed its political fights within its government system.

Role of women

Main article: Women in the Mexican–American War

Mexican women had important roles during the war. Some women, called soldaderas, traveled with soldiers to help them. They did not fight in big battles, but some helped when their cities were defended. Others cared for wounded soldiers from both sides. Two women, Doña Jesús Dosamantes and María Josefa Zozaya, are remembered for their bravery.

At home, Mexican women showed support in different ways, such as wearing special clothing and making serious paintings.

American women also helped during the war. Some, like Sarah Bowman, gave food and cared for injured soldiers. Others stayed in Mexico to look after their businesses while their husbands were away. In the United States, women showed support by making items for soldiers and speaking up about the war. Journalists like Anne Royall, Jane Swisshelm, and Jane Cazneau helped share women's views about the war.

Outbreak of hostilities

Texas campaign

Main article: Texas Campaign

Thornton Affair

President Polk sent General Taylor and his soldiers south to the Rio Grande. Taylor built a small fort called Fort Brown/Fort Texas) near the city of Matamoros, Tamaulipas.

Mexican forces got ready for war. On April 25, 1846, Mexican soldiers attacked a small group of American soldiers led by Captain Seth Thornton. This event is called the Thornton Affair. The Mexican soldiers defeated the American group, and some American soldiers were hurt or captured.

Siege of Fort Texas

A few days after the Thornton Affair, Mexican soldiers began surrounding Fort Texas on May 3, 1846. They fired at the fort, and the American soldiers fired back. The fighting went on for many hours, and some American soldiers were hurt.

Battle of Palo Alto

On May 8, 1846, General Zachary Taylor arrived with more soldiers to help the fort. But a Mexican general named Arista met them near Brownsville, Texas. The American soldiers used fast-moving cannons on horses, which were very effective. The Mexican soldiers tried to fight back but had to move to a better position during the night.

Battle of Resaca de la Palma

The next day, on May 9, 1846, the two sides fought fiercely in the Battle of Resaca de la Palma. The American soldiers captured the Mexican cannons, and the Mexican soldiers had to retreat. Many Mexican soldiers were hurt, and some drowned trying to cross the Rio Grande. General Taylor then moved his soldiers into Mexican territory.

Declarations of war, May 1846

President Polk told Congress that Mexico had attacked American soldiers on American land, so he asked for a declaration of war. The U.S. Congress agreed to declare war on May 13, 1846. Some politicians disagreed, but most supported the war.

In Mexico, their Congress officially declared war later, on July 7, 1846.

General Santa Anna's return

After losing battles, Mexico asked General Santa Anna to come back to help. He had been living in Cuba but agreed to return to defend Mexico. Santa Anna focused on leading Mexico's army instead of governing the country. Some Mexican states did not support him.

Reaction in the United States

Opposition to the war

In the United States, people had different feelings about the war. Many Whigs, especially in the North, did not like the war. They were worried it would spread slavery to new places. Former President John Adams spoke against the war.

Exiled abolitionist Frederick Douglass also spoke out against the war. Some Whigs, like Joshua Giddings and Abraham Lincoln, questioned President Polk’s reasons for starting the war. Lincoln asked for proof that the fighting happened on American land.

Support for the war

Many Democrats, especially in the South, supported the war. They thought it was America’s destiny to grow westward. President Polk said that Mexico had attacked American land and that the United States needed to protect its claims in New Mexico and California.

U.S. journalism during the war

This was the first time the United States had so much news coverage of a war. Reporters sent updates from the battlefield, and new inventions like the telegraph helped share news fast. Writers and artists shared their views, with some strongly supporting the war. The news helped unite Americans and celebrate victories. Generals like Taylor and Scott became popular heroes.

U.S. invasions on Mexico's periphery

See also: Mexican–American War campaigns

New Mexico campaign

After war began on May 13, 1846, United States Army General Stephen W. Kearny moved southwest from Fort Leavenworth, Kansas, in June 1846 with about 1,700 soldiers. His mission was to secure the lands of Nuevo México and Alta California.

In Santa Fe, Governor Manuel Armijo wanted to avoid fighting, but some local leaders forced him to prepare for battle. Armijo planned to defend at Apache Canyon but changed his mind before the American army arrived. Some leaders wanted to fight, but Armijo ordered them to stop. The local army moved back to Santa Fe, and Armijo fled.

Kearny and his soldiers arrived on August 15 and entered Santa Fe without any fighting. He claimed the New Mexico Territory for the United States and set up a new government.

After leaving for California, some people in Santa Fe planned to fight back. On January 19, 1847, they started a revolt in Taos, New Mexico, called the Taos Revolt. They attacked a leader’s home and later a mill. The U.S. army quickly moved to stop the revolt and defeated the rebels.

California campaign

Main article: Conquest of California

News of the war reached California in August 1846. Some American settlers took control of a Mexican outpost in Sonoma on June 14, 1846, and raised a flag. More joined them, and they prepared for possible fighting.

U.S. forces arrived and took control of several cities. After some battles, the fighting ended with an agreement in January 1847.

Pacific Coast campaign

Main article: Pacific Coast Campaign

U.S. ships took control of ports along the coast and cleared the area of enemy ships. They captured several places and defeated local forces.

Northeastern Mexico

Main articles: Battle of Monterrey and Battle of Buena Vista

Battle of Monterrey

U.S. troops under Zachary Taylor crossed the Rio Grande and moved toward Monterrey, Nuevo León. After a tough battle, they took the city but allowed Mexican forces to leave. Taylor later occupied another city, Saltillo.

Battle of Buena Vista

Later, Mexican forces under Santa Anna attacked Taylor’s smaller army. After a hard fight, Taylor’s troops held their position, and Santa Anna decided to withdraw.

Northwestern Mexico

In late 1846, U.S. forces moved into areas now part of northwest Mexico. They had some battles but faced little resistance from local people, who had already been affected by raids from Native groups.

Southern Mexico

The southern part of Mexico had many Native people and was far from the capital. The U.S. Navy helped by blocking ports and supporting troops. There were some battles along the coast, and local groups sometimes fought against both Mexican and U.S. forces.

Scott's invasion of Mexico's heartland

Landings and siege of Veracruz

Main article: Siege of Veracruz

President Polk sent General Winfield Scott with another army to invade Mexico from the coast. Scott’s troops sailed to the port of Veracruz to begin an invasion aimed at taking Mexico City. On March 9, 1847, Scott made one of the first big sea landings in U.S. history to get ready for a siege. About 12,000 soldiers landed near the walled city using special boats. Future leaders like Robert E. Lee, George Meade, Ulysses S. Grant, James Longstreet, and Thomas “Stonewall” Jackson were part of this force.

Veracruz was defended by Mexican General Juan Morales with 3,400 soldiers. U.S. ships used bombs and guns to break down the city walls. After a 12-day siege, the city surrendered. U.S. troops lost some soldiers, and Mexico lost some too. Many civilians were also hurt. During the siege, some U.S. soldiers got very sick from a disease called yellow fever.

Advance on Puebla

Main article: Battle of Cerro Gordo

Mexican leader Santa Anna let Scott’s army move inland, hoping diseases would slow them down. He picked Cerro Gordo to fight, thinking the land would help his troops. Scott’s soldiers took a different path through tough terrain and surprised the Mexicans. In the battle on April 18, the Mexican army was defeated. After this loss, the Mexican army kept trying to fight.

Pause at Puebla

On May 1, 1847, Scott moved to Puebla, Mexico’s second-largest city. The city gave up without fighting because people were scared of possible attacks. Scott tried to keep his soldiers from hurting people and treated locals fairly to keep peace.

Advance on Mexico City and its capture

Main article: Battle for Mexico City

Scott left a small group behind and moved toward Mexico City on August 7. After several battles, including the Battle of Chapultepec, the capital fell. During the Battle of Chapultepec, some young Mexican soldiers stayed to fight even though it was very dangerous. Their bravery became famous in Mexico.

Santa Anna's last campaign

In late September 1847, Santa Anna tried one last time to stop the U.S. Army by surrounding them. But his plan failed, and his troops scattered when they couldn’t get enough food.

Occupation of Mexico City

After taking Mexico City, U.S. forces stayed there but faced attacks from local fighters. These fighters, called guerrillas, tried to push back against the U.S. Army. General Scott protected his troops and set up posts to keep supply lines safe.

Desertions

Many soldiers in both armies left their units. In the Mexican Army, most were farmers who missed their homes and families. In the U.S. Army, some soldiers left. Some joined the Mexican side, especially recent immigrants from Europe. Others just wanted to go home or find better conditions.

San Patricios

The most famous group to leave the U.S. Army was the Saint Patrick’s Battalion, made up mostly of Irish and German Catholic immigrants. They left because of unfair treatment and tough conditions. Most were killed in battle, and those captured were tried and punished. Their leader, John Riley, was marked as a criminal. A memorial in San Angel remembers them today.

End of war, terms of peace

Mexico had a hard time defending itself during the war because many cities and its capital were taken over. Ending the war officially was tough because of disagreements inside Mexico. Peace started in January 1847 in Alta California with the Treaty of Cahuenga. In this treaty, local Mexican residents agreed to stop fighting American forces. A full peace treaty was needed to end the whole war.

The Treaty of Guadalupe Hidalgo was signed on February 2, 1848. This treaty ended the war. It gave the United States control of Texas and set the U.S.–Mexican border along the Rio Grande. The treaty also added large areas to the United States. These areas include parts of what are now California, Nevada, and Utah, as well as parts of New Mexico, Arizona, Colorado, Texas, Oklahoma, Kansas, and Wyoming. In return, Mexico got $15 million, and the United States agreed to pay $3.25 million for debts Mexico owed to American citizens. Both the U.S. Senate and the Mexican government approved the treaty.

The lands the United States gained are often called the Mexican Cession. The treaty also promised to help protect people in the area from attacks, but these promises were not always kept. The treaty ended a long and hard war between the two nations.

Main article: All of Mexico Movement

Aftermath

Altered territories

Before the Mexican-American War, Mexico owned a lot of land, but by 1849, it lost more than half of it. This included parts of what are now the U.S. states of California, New Mexico, and others. The land was often empty but had many Native American groups living there. After the war, many of these Native groups stayed in the new U.S. lands.

The new American settlers changed the laws in these areas. They kept some good ideas from Mexican law, like fair rules about sharing property and managing water. But many Mexicans and Native Americans lost important rights, like the right to vote or hold office. Some Native groups lost their land and were forced to move.

Effect on the United States

The war made many Americans feel proud of their country. It helped the idea that the United States was meant to grow and expand, called Manifest Destiny. Even though some people had opposed the war, one of the generals who fought in it, Zachary Taylor, became president because of his success.

The war also helped train many leaders who later fought in the Civil War. Men like Ulysses S.. Grant and Robert E. Lee learned important skills that they used later. Grant later wrote that he thought the war was unfair to Mexico and that it caused problems for the United States, including the Civil War.

Effect on the American military in the Civil War

Many important leaders in the Civil War had fought in the Mexican-American War. They learned how to lead soldiers and plan battles. For example, Ulysses S. Grant, who later became president, served under General Zachary Taylor and learned many useful skills. Robert E. Lee, who led the Confederate forces, also gained experience fighting in Mexico.

Social and political context

The war caused big debates in the United States about slavery. Some people wanted to prevent slavery from spreading to the new lands the United States gained. This disagreement about slavery became a major issue that later helped cause the Civil War. The war also made some Americans feel better about their country, but it also increased unfair treatment of Mexicans and Native Americans.

Veterans of the war

After the Civil War, veterans of the Mexican-American War started asking for help from the government. They wanted pensions, which are payments to help them when they got older. It took many years, but in 1887, the government finally agreed to give pensions to these veterans who had served their country.

Effects on Mexico

For Mexico, the loss in the war was very painful. The country lost a lot of land and faced many internal problems. After the war, Mexico went through more conflicts, including a war between different political groups and an invasion by France. Leaders in Mexico tried to understand why they lost and what they could do to improve. Some leaders, like Santa Anna, were blamed for the loss and later went into exile.

Legacy

Mexico

After the French left Mexico in 1867, Mexico began to remember the Mexican–American War. The story of the Niños Héroes, young cadets who fought bravely at the Battle of Chapultepec, became important. Their sacrifice was honored with a small memorial in 1881. Over time, bigger monuments were built, including one at the entrance to Chapultepec Park in Mexico City, finished in 1952. By this time, the United States and Mexico were friends and worked together.

United States

In the United States, the war was often forgotten after the Civil War. However, some monuments were built to remember it, like one for the Palmetto Regiment in South Carolina in 1858. A painting in the U.S. Capitol Building shows U.S. soldiers entering Mexico City. The Marine Corps Hymn mentions "From the Halls of Montezuma," remembering the war. There is a cemetery in Mexico City for U.S. soldiers who died during the war, maintained by the American Battle Monuments Commission. The Mormon Battalion also put up monuments in Utah and Los Angeles to honor their role in the war.