"...four years spent in the north of Mexico had surprisingly not taken its toll on Diaz's small but substantial army, which controlled a wide swath of the arid north and much of the highlands of the Sierra Madres. This was the land of El Caudillo del Norte, as he came to be known, a folk hero standing against the Imperial throne and continuing the War of Reform long after it had been ended in the monarchy's favor in the south. Young, swaggering and handsome, Diaz led raids against the small expeditions Maximilian I would send north to find him. Little more than a nuisance for much of the early Empire, by early 1867, however, Diaz had begun to regroup and amass serious forces again. Escaped slaves from the Confederacy, especially from Texas and Louisiana, had sought shelter in Mexico, a land that had abolished slavery decades earlier. Indigenous Mexicans and poor mestizos were drawn to his championing of land reform and the unfinished Juarez project; while most liberals, moderate and radical, had since 1863 accepted Maximilian and taken amnesties, Diaz and his supporters had not. "The foreign crown shall be driven from Chapultepec while I still draw breath!" Diaz declared in a fiery speech in Chihuahua on Christmas Day 1866, the day after his forces had surprised the garrison there at night and seized the city. It was the boldest move made by the suddenly reenergized rebels since Juarez's death.
Alarmed, Emperor Maximilian dispatched in early January a force from Mexico City to head north and retake Chihuahua, and immediately sent additional forces to reinforce northern cities, particularly the crucial and booming port of Matamoros at the mouth of the Rio Grande and on the border with Texas. Well aware that Diaz's men had conducted raids into Texas and the Arizona Territory over the last few years as well, and with Mexican newspapers suddenly shrieking with alarm that the war might bloom again after four years of relative peace in the south, the Emperor's men began putting out feelers to foreign mercenaries, hoping to not have to dispatch the still-reforming and developing Mexican Army, in the midst of a grand overhaul to professionalize in the mold of Prussia or Austria's forces, northwards until it was absolutely necessary.
It fell then to Forrest, who in January of 1867 gathered a surprising force in New Orleans, to set sail to Matamoros and then ride inland - two hundred veterans of the Memphis Massacre, known as the Tennessee Templars; forty Cherokee volunteers recruited from the Indian Territory; and three hundred additional volunteers, all veterans of the War of Independence from Louisiana and Mississippi, short on pay and eager for glory when a grand purse was offered by Mexico for Diaz's capture or execution. Upon arriving in Matamoros, they were greeted by an additional three dozen German Texan volunteers, some of whom had been robbed by Diaz's "bandidos," twenty Texas Rangers, and well over a hundred Mexicans, some of them criminals and one or two escaped slaves. In all, Forrest's force numbered over 700, and became dubbed "the Great Posse." Westward they rode, at rapid pace, Forrest back in his element in the saddle, hoping to find Diaz before any of the other mercenary bands setting out or the Mexican Imperial Army did. The Sierra Madre War had begun."
- The Wizard: The Life of Nathan Forrest (University of Mississippi, 1927)