In early March of 2016, the bodies of eight electrical company employees and three farmers were found hacked-up and bullet-riddled near a desolate field in El Salvador’s San Juan Opico municipality.

The wanton force involved – the killers used machetes and machine guns – bore all the hallmarks of MS-13, or Mara Salavtrucha, the uber-violent street gang that started in California but has since spread like a plague throughout Central America.

“These two gangs have turned the Central American northern triangle into the area with the highest homicide rate in the world." — Justice Department report

Authorities in El Salvador were quick to fix blame on the gang and President Salvador Sánchez Cerén swiftly implemented a package of "extraordinary measures" to crack down on violent crime.

The only problem was that it wasn’t MS-13 that carried out the massacre. It was a gang known as Barrio 18.

While authorities can be forgiven for mixing up the two – both have members covered in head-to-toe tattoos, are well known for their murderous tactics and originated in some of the same Los Angeles neighborhoods – MS-13 and Barrio 18 are bitter rivals whose ongoing feud is responsible for the deaths of thousands across the U.S., Mexico and Central America.

“These two gangs have turned the Central American northern triangle into the area with the highest homicide rate in the world,” a 2013 Justice Department report on gang violence noted.

While some trace the gang’s origins as far back as the 1950s, Barrio 18 truly came into being in the 1980s when it broke away from one of California’s oldest Hispanic gangs, Clanton 14.

Barrio 18 originally was composed of Mexican immigrants or people of Mexican descent, but soon began incorporating other Latino nationalities as Los Angeles’ immigrant community diversified.

In the late 1990s, through a series of raids the FBI and local law enforcement were able to arrest a number of Barrio 18’s leaders. These raids were meant to cause the gang’s demise, but the detention of its capos gave Barrio 18 a new base for recruitment: the U.S. prison system.

Coinciding with the gang’s rise to power in U.S. prisons was its spread southward through Mexico and Central America as U.S. immigration officials increased the number of criminal offenses that could lead to deportation.

The high numbers of gang members being deported paired with relatively weak governments in Central America helped Barrio 18 and MS-13 become potent criminal forces in El Salvador, Honduras and Guatemala.

Both gangs make their livings through kidnapping, small-time drug trafficking, running brothels, money laundering and contract killings.

“Like its better known rival, [MS-13], the Barrio 18 has cells operating from Central America to Canada, including the United States,” the organized-crime investigative nonprofit Insight Crime noted. “With thousands of members across hundreds of kilometers, and interests in a number of different illicit activities, Barrio 18 is one of the more significant emerging criminal threats in the region.”

In 2012, the violence between the two gangs hit endemic levels and El Salvador – a country about the size of Massachusetts -- was averaging 14 murders per day. To quell the bloodshed, the Catholic Church and the government stepped in and were able to mediate a shaky truce between MS-13 and Barrio 18.

The truce, however, fell apart in 2014 and violent crime in the country continued to swell until another pact in April of last year – bolstered by Sánchez Cerén’s security crackdown – saw homicide rates start to drop.

The gangs still make El Salvador one of the most dangerous countries in the world, as the Opico massacre shows, and the security crackdown has caused many gang members to move to neighboring Guatemala and Honduras.

In the U.S., the tensions between Barrio 18 and MS-13 may not be leaving as long a trail of dead bodies as in Central America, but both gangs have made their presence known in almost every state and major metropolitan region.

Barrio 18 is believed to operate in around 120 cities in 30 states, but has made its presence most felt in its home state of California. Much of the street crime in Los Angeles County is believed to be related to the gang and federal law enforcement said that while street-level drug dealing is Barrio 18’s main income source, the group has been linked to murders, assaults, arson, copyright infringement, extortion, human trafficking, illegal immigration, kidnapping, prostitution, robbery and weapons trafficking.

In one of Barrio 18’s most gruesome and highly publicized crimes on American soil, Catarino Gonzalez – a then-23-year-old gang member, was sentenced in 2001 to life in prison for shooting an LA police officer in the head while he sat in a patrol car.