The Mexican-American War (1846-1848) was fought from California to Mexico City and many points in between. There were several main engagements: the American army won all of them. Here are some of the more important battles fought during that bloody conflict.
The first major battle of the Mexican-American War took place at Palo Alto, not far from the US/Mexico border in Texas. By May of 1846, a series of skirmishes had flared into all-out war. Mexican General Mariano Arista laid siege to Fort Texas, knowing that American General Zachary Taylor would have to come and break the siege: Arista then laid a trap, picking the time and place the battle would take place. Arista did not, however, count on the new American "Flying Artillery" which would be the deciding factor in the battle.
The next day, Arista would try again. This time, he laid an ambush along a creekbed with a great deal of dense vegetation: he hoped the limited visibility would limit the effectiveness of the American artillery. It worked, too: the artillery was not as much of a factor. Still, the Mexican lines did not hold against a determined assault and the Mexicans were forced to retreat to Monterrey.
General Taylor continued his slow march into the Mexican north. Meanwhile, Mexican General Pedro de Ampudia had heavily fortified the city of Monterrey in anticipation of a siege. Taylor, defying conventional military wisdom, divided his army to attack the city from two sides at once. The heavily fortified Mexican positions had a weakness: they were too far apart from one another to offer mutual support. Taylor defeated them one at a time, and on September 24, 1846, the city surrendered.
After Monterrey, Taylor pushed southwards, making it as far as a little bit south of Saltillo. Here he paused, because many of his troops were to be reassigned to a planned separate invasion of Mexico from the Gulf of Mexico. Mexican General Antonio Lopez de Santa Anna decided on a bold plan: he would attack the weakened Taylor instead of turning to meet this new threat. The Battle of Buena Vista was a fierce battle, and probably the closest the Mexicans came to winning a major engagement. It was during this battle that the St. Patrick's Battalion, a Mexican artillery unit comprised of defectors from the American army, first made a name for itself.
For American President James Polk, the object of the war was to acquire Mexico's northwestern territories including California, New Mexico and much more. When the war broke out, he sent an army westward under General Steven W. Kearny to make sure those lands were in American hands when the war ended. There were many small engagements in these contested lands, none of them very large-scale but all of them determined and hard-fought. By early 1847 all Mexican resistance in the region was over.
In March of 1847, the US opened a second front against Mexico: they landed near Veracruz and marched on Mexico City in the hopes of ending the war swiftly. In March, General Winfield Scott oversaw the landing of thousands of American troops near Veracruz on Mexico's Atlantic coast. He promptly laid siege to the city, using not only his own cannons but a handful of massive guns he borrowed from the navy. On March 29, the city had seen enough and surrendered.
Mexican General Antonio López de Santa Anna had regrouped after his defeat at Buena Vista and marched with thousands of determined Mexican soldiers towards the coast and the invading Americans, He dug in at Cerro Gordo, or “Fat Hill,” near Xalapa. It was a good defensive position, but Santa Anna foolishly ignored reports that his left flank was vulnerable: he thought the ravines and dense chaparral to his left made it impossible for the Americans to attack from there. General Scott exploited this weakness, attacking from a trail hastily cut through the brush and avoiding Santa Anna's artillery. The battle was a rout: Santa Anna himself was nearly killed or captured more than once and the Mexican army retreated in disarray to Mexico City.
The American army under General Scott inexorably made its way inland towards Mexico City. The next serious defenses were set around the city itself. After scouting the city, Scott decided to attack it from the southwest. On August 20, 1847, one of Scott's Generals, Persifor Smith, detected a weakness in the Mexican defenses: Mexican General Gabriel Valencia had left himself exposed. Smith attacked and crushed Valencia’s army, paving the way for the American victory at Churubusco later in the same day.
With Valencia's force defeated, the Americans turned their attention to the city gate at Churubusco. The gate was defended from a fortified old convent nearby. Among the defenders was the St. Patrick's Battalion, the unit of Irish Catholic deserters who had joined the Mexican army. The Mexicans put up an inspired defense, especially the St. Patrick's. The defenders ran out of ammunition, however, and had to surrender. The Americans won the battle and were in a position to threaten Mexico City itself.
After a brief armistice between the two armies broke down, Scott resumed offensive operations on September 8, 1847, attacking a heavily fortified Mexican position at Molino del Rey. Scott assigned General William Worth the task of taking the fortified old mill. Worth came up with a very good battle plan which protected his soldiers from enemy cavalry reinforcements while assaulting the position from two sides. Once again, the Mexican defenders put up a valiant fight but were overrun.
With the Molino del Rey in American hands, there was only one major fortified point between Scott's army and the heart of Mexico City: a fortress at the top of the Chapultepec hill. The fortress was also Mexico's Military Academy and many of the young cadets fought in its defense. After a day of pounding Chapultepec with cannons and mortars, Scott sent parties with scaling ladders to storm the fortress. Six Mexican cadets fought valiantly to the end: the Niños Héroes, or "Hero boys" are honored in Mexico to this day. Once the fortress fell, the city gates were not far behind and by nightfall General Santa Anna had decided to abandon the city with those soldiers that he had left. Mexico City belonged to the invaders and Mexican authorities were ready to negotiate. The Treaty of Guadalupe Hidalgo, approved in May of 1848 by both governments, ceded vast Mexican territories to the USA including California, New Mexico, Nevada and Utah.