Based on an incident on June 21, 1916, when American forces pursuing bandit Pancho Villa in Mexico were confronted by a Mexican army unit--which was also hunting Villa--near the town of Carrizal and a gun battle erupted. Ten US troops and 45 Mexican soldiers were killed.
The earliest known example of a "black western", being about a soldier in the 10th Cavalry Regiment, an all-black unit (with white officers) in the US army, which was segregated at the time.
Lincoln Motion Picture Company reportedly hired around 300 extras throughout the course of production.