In 1841, during his second term as governor, Armijo was tasked with confronting a threat from the east — not from the United States or France but from the Republic of Texas.

American-born Texans were in an expansionist mood that year and felt they would need room to grow their newly minted republic. New Mexico seemed ripe for the taking. Word reached Santa Fe of a contingent of Tejanos moving west toward the New Mexico border. Armijo amassed an army of Mexican New Mexicans and led them east to head off the invading army. This was the Texas-Santa Fe Expedition.

The Texans, who numbered about 300, were not prepared for the harsh terrain, nor for the vast, empty distances of western Texas and eastern New Mexico. Their miscalculations would dearly cost them dearly.

The brave contingent of New Mexicans was able to easily overtake and overcome its adversaries, who were in bad shape and half starving by the time the New Mexicans encountered them. Armijo took the Texans prisoners, and they were marched south to be imprisoned first in Mexico City, then in Veracruz, Mexico.