It is an open post, without either stockades or breastworks of any kind, and, barring the officers and soldiers who are seen about, it has much more the appearance of a quiet frontier village than that of a military station.

The huts are built of pine logs, obtained from the neighboring mountains, and the quarters of both officers and men wore a neat and comfortable appearance.

In New Mexico, the U.S. army set up garrisons in settlements to protect the area’s inhabitants and travel routes from raids by Native Americans, but this proved unsatisfactory.

For a decade it served as the base for military operations in the area and a key station on the Santa Fe Trail, affording travelers a place to rest nearby and refit at the post sutler’s store (where general merchandise not supplied to soldiers by the army was sold).

During the 1850s, the fort’s mounted riflemen (called dragoons) campaigned against several southern Rocky Mountain Indian tribes that were disrupting traffic on the Santa Fe Trail.

Canby, charged with the territory’s defense, concentrated troops at Fort Craig on the Rio Grande near present-day Socorro, and sent its soldiers to patrol the Santa Fe Trail, the main artery of supply for federal forces.

When the Civil War began in April 1861, most of the regular troops (except those officers who joined Confederate forces) were withdrawn from Fort Union and other frontier posts to be sent east.

The second fort at the national monument was designed to defend against a Confederate military invasion coming north up the Rio Grande Valley, from El Paso, Texas.

Defeated, the Confederates withdrew to Texas, ending Civil War activity in the Southwest and saving the mines in Colorado from being used as a source of funds for the South.

Several relentless campaigns against the Apaches, Navajos, Cheyennes, Arapahos, Kiowas, Utes, and Comanches finally brought peace to the Southern Plains in the spring of 1875 on the government's terms.

Fort Union's involvement in the Indian wars had come to an end, but its garrison occasionally helped to track down outlaws, quell mob violence, and mediate feuds.

The following year, Colonel Edwin Vose Sumner expanded the fort to an area of eight square miles by claiming the site as a military reservation.