Fed up with this situation, armed “self-defense” groups began to appear in Michoacán in February 2013. Their members come from various walks of life, including small ranchers, business people and emigrants returning from the United States.

These associations of vigilantes are not the first to take justice into their own hands in Michoacán. Three years ago, the Indian community of Cherán decided to disown the local (ineffective and corrupt) authorities, dig trenches and post armed guards at the entrances to their village property in order to resist the depredations of illegal wood-cutters decimating their forest reserves, the millennial patrimony of the community.

The epicenter of the present vigilante confrontation with the Knights Templar is the area known as the Tierra Caliente, a relatively isolated zone that, since colonial times, has been marked by its torrid climate, fertile soil, aggressive animals, poisonous plants, and a tendency toward violence among its inhabitants. Fray Diego Basalenque, who composed chronicles of Michoacán in the 17th century, wrote about the Tierra Caliente: “For someone not born here, it is uninhabitable. For its natives it is unbearable.” It has become a preferred sanctuary for the Knights.

The national government recently sent a substantial federal force (both military and police) to the region. Corrupt municipal police officers have been stripped of their authority and national troops have established a modus vivendi with self-defense groups. The vigilantes have the support of the majority of the population and of respected clerics.

Unverified rumors have it that some of the self-defense units are connected with a narco gang in a neighboring state called Jalisco New Generation Cartel (Cártel de Jalisco Nueva Generación). Regardless of whether that is true or not, President Enrique Peña Nieto, who came to power in 2012, would be wise to press for the incorporation of the vigilantes into a legal entity, as two powerful presidents in the 19th century, Benito Juárez and Porfirio Díaz, did when they were dealing with crime. They developed a mobile strike force (Los Rurales) that suppressed rampant banditry. The elimination of a gang like the Knights Templar, however, will require much intelligence-gathering and coordination among various law-enforcement agencies. And it will take time.

After the recent seizure of Knights Templar safe houses in a Michoacán village, the vigilantes displayed some confiscated items, including a sword encrusted with diamonds said to have belonged to the Knights’ paramount leader and to have been used in a “religious” ceremony imposing total commitment on new members of the gang.

The vigilantes believe their actions are necessary to combat the outrageous wealth, extortion and savagery of the Knights. They say their goal is to clear out the gang, village by village, town by town. The strategy is working: In the city of Zamora, for the last 15 days gas stations and other businesses have been free from extortion. The vigilantes have let it be known that their next objective is the principal city of the Tierra Caliente, Apatzingán, where the Knights are deeply entrenched. If they can take back control of Apatzingán, the vigilantes will doubtless feel a provisional sense of “mission accomplished” — appropriate enough in the town where, in 1814, Mexico’s first constitution was proclaimed.

Enrique Krauze is a historian, the editor of the literary magazine Letras Libres and the author of “Redeemers: Ideas and Power in Latin America.” This article was translated by Hank Heifetz from the Spanish.