A Huertista was a soldier fighting under, and in support of, Victoriano Huerta, the revolutionary general responsible for the arrest and shooting of Francisco Madero in 1913. After the deposition of Madero, Huerta served as president of Mexico until July 1914 when he was forced to resign and fled the country.
He spent a year and half in exile before dying of cirrhosis in a Texan prison.
Huerta is still vilified by modern-day Mexicans, who generally refer to him as El Chacal ('The Jackal’).
The German captain Wirtz who sucks out the eyeballs of the rebel soldier is an interesting one. McCarthy may have been partly inspired by Heinrich Hartmann Wirz (better known as Henry Wirz), the Swiss-born Confederate officer tried and executed in the aftermath of the American Civil War for mistreatment of Union soldiers during his command of the Andersonville prison camp.
Besides the similarity in their names and cruelty towards prisoners, both men were foreigners occupying positions of power in a country not of their birth, and both multilingual (the fictional Wirtz 'spoke Spanish well for all he spoke it with a German accent', while Wirz was fluent in English, German and Dutch).
Warning: The embedded video contains some disturbing images.