To reinforce the American claim that the border was at the Rio Grande, the US commander in Texas, Brigadier General Zachary Taylor, sent troops to the river to construct Fort Texas in March 1846. On May 3, Mexican artillery commenced a weeklong bombardment, killing two, including the fort’s commander, Major Jacob Brown. Hearing the sound of firing, Taylor began to move his 2,400-man army to the fort’s aid, but was intercepted on May 8, by a force of 3,400 Mexicans commanded by General Mariano Arista.
When the Battle of Palo Alto opened, the Mexican line stretched nearly a mile long. With the enemy spread thin, Taylor opted to utilize his light artillery rather than make a bayonet charge. Employing a tactic known as “Flying Artillery,” developed by Major Samuel Ringgold, Taylor ordered the guns to advance in front of the army, fire, and then quickly and frequently change position. The Mexicans were unable to counter and suffered around 200 casualties before retiring from the field. Taylor’s army suffered only 5 killed and 43 wounded. Unfortunately, one of the wounded was the innovator Ringgold, who would die three days later.
Departing Palo Alto, Arista withdrew to a more defensible position along a dry riverbed at Resaca de la Palma. During the night he was reinforced bringing his total strength up to 4,000 men. On the morning of May 9, Taylor advanced with a force of 1,700 and began to assault Arista’s line. The fighting was heavy, but American forces prevailed when a group of dragoons was able to turn Arista’s flank forcing him to retreat. Two subsequent Mexican counterattacks were beaten off and Arista’s men fled the field leaving behind a substantial number of artillery pieces and supplies. American casualties numbered 120 killed and wounded, while the Mexicans numbered over 500.
During the summer of 1846, Taylor’s “Army of Occupation” was heavily reinforced with a mix of regular army and volunteer units, raising its numbers to over 6,000 men. Advancing south into Mexican territory, Taylor moved towards the fortress city of Monterrey. Facing him were 7,000 Mexican regulars and 3,000 militia commanded by General Pedro de Ampudia. Beginning on September 21, Taylor tried for two days to breach the city’s walls, however his light artillery lacked the power to create an opening. On the third day, several heavy Mexican guns were captured by forces under General William A. Worth. The guns were turned on the city, and after savage house to house fighting, Monterrey fell to American forces. Taylor trapped Ampudia in the plaza, where he offered the defeated general a two month ceasefire in exchange for the city.
Despite the victory, President Polk was livid that Taylor had agreed to a ceasefire, stating that it was the army’s job to “kill the enemy” and not to make deals. In the wake of Monterrey, much of Taylor’s army was stripped away to be used in an invasion of central Mexico. Taylor was overlooked for this new command due to his behavior at Monterrey and his Whig political leanings (he would be elected President in 1848). Left with 4,500 men, Taylor ignored orders to stay at Monterrey and in early 1847, advanced south and captured Saltillo. Upon hearing that General Santa Anna was marching north with 20,000 men, Taylor shifted his position to a mountain pass at Buena Vista. Digging in, Taylor’s army beat off Santa Anna’s repeated attacks on February 23, with Jefferson Davis and Braxton Bragg distinguishing themselves in the fighting. After suffering losses of close to 4,000, Santa Anna withdrew, essentially ending the fighting in northern Mexico.