Fort Marcy was a military reservation in New Mexico. In May 1846 the United States declared war on the Republic of Mexico after a dispute arose over the location of the southern border of the newly annexed State of Texas. Led by General Stephen W. Kearney, his Army of the West, with approximately 1,700 troops, marched into the city of Santa Fe to claim the city and the entire New Mexico Territory on August 18, 1846.