Sibley resigned from the US Army as he sided with the Confederacy. Placed in command of a brigade of volunteer cavalry in West Texas, Sibley dubbed his small force the Army of New Mexico and began planning a New Mexico Campaign to capture the cities of Albuquerque and Santa Fe and Fort Union on the Santa Fe Trail to establish a forward base of supply. He then intended to continue north to Colorado to capture the numerous gold and silver mines in the area as a means of replenishing the badly depleted Confederate treasury. From there, Sibley planned to join forces with Confederate Lieut. John R. Baylor, already in control of much of southern New Mexico and Arizona territories and headquartered in Tucson, AZ. Their ultimate strategy was to gain access to the warm-water ports of California and establish a badly needed supply line to the South, as the Union Navy had implemented a naval blockade from Virginia to Texas. Throughout the 1862 New Mexico campaign, his opponent was Colonel Edward Canby, formerly a comrade in arms in the U.S. Army. Some historians have said he was Sibley's brother in law, but this relation has been disputed.