In 1862, the Confederacy claimed the southern tract of the New Mexico Territory, which includes the southern halves of modern-day Arizona and New Mexico. Their goal was to gain control of a portion of the southwest as a means to reach the Union state of California.
The decisive battle of the New Mexico Campaign took place in March, 1862 at Glorieta Pass, in northern New Mexico. There were small skirmishes on the 26th, as Union troops took control of Apache Canyon, at one end of the Pass. No fighting occurred on the 27th as reinforcements for both sides arrived.
The critical fighting took place on the 28th. Despite early Union success, by late afternoon the Confederates had control of the battlefield and were poised for victory. The tide was turned when Union scouts discovered the Confederate’s supply train standing relatively unguarded at nearby Johnson’s Ranch. Union soldiers captured the train, looted it extensively, and destroyed what they could not carry. With no supplies left to sustain their troops, the Confederates were forced to retreat, first to Santa Fe, and then further east to San Antonio. The Union victory at Glorieta Pass effectively ended the Confederate’s bid to control the Southwest.