In a series of battles American forces first led by General Kearny and then Colonel Doniphson captured New Mexico territory. American forces then were split, some heading for California and the balance to Mexico.
Texas claimed New Mexico. President Polk directed the governor of Missouri to raise an army for the conquest of New Mexico. Colonel Stephen Watts Kearny was placed in command of the army which number 856 Missouri volunteers. when it set out. Colonel William Doniphsan was elected colonel of the regiment. Besides the Missouri volunteers Kearny had two companies of artillery and other units bringing his total forces to 1658. The American forces headed toward Sante Fe and trained as they went. On July 22 the American forces reached Bent's Fort. At that point Kearny attempted to convince the Mexican commander Armijo to give up without a fight. Armijo did not give an immediate answer, finally deciding to fight. On August 16th Armijo marched his troops to Apache Canyon. Armijo was not able to hold his forces together, and thus on the next day he withdrew. The next day Kearny marched through the pass and on to Sante Fe New Mexico’s capital. There he declared it American territory. Kearny then divided his force into three. The first group under his command headed to California to capture it. The second group would garrison Sante Fe and the third under Doniphson would put down local Indians and then head South into Mexico. Doniphson quickly signed treaties with local Indians, then headed South at end of November. In January there was an uprising against the American forces but it was decisively put down by Colonel Sterlin Price in a series of battle that culminated at Taos.
Doniphon then headed south. His force headed south along the Rio Grande through the heat. When they reached El Paso a force of Mexicans were waiting for them under the command of Captain Ponce de Leon. Leon demanded that Doniphon surrender or his forces would charge and annihilate the American force. Doniphons answer: “Charge and be damned”. The Mexican charged. 100 Mexican were killed, Doniphons forces lost 7 men wounded. Doniphans next step was Chihuahua City. There a large Mexican force awaited them. 1200 cavalry, 1500 infantry and 1000 ranchers who were commanded by Brigadier General Jose Antonio de Heredia. Doniphan viewed the Mexican defenses, and decided circle the defenses and try to attack from the rear. The Mexican thought that the Americans were going to bypass the city, and they decided to attack the American forces. The Americans answered with artillery fire, and a duel resulted. The American shot was more accurate and the Mexican fire died down. The American forces then attacked the Mexican fortification. 300 Mexicans were killed and another 300 were wounded against American losses of 1 killed and five wounded. The balance of the American forces fled.