Mexico's drug trade is worth up to $29 billion a year, the FBI says, and has resulted in the brutal murders of at least 100,000 people.

Last year alone, nearly 20,000 people were killed, while 27,000 lost their lives in 2011 at the height of the conflict — that is about 75 people every day.

Torture, beheadings and mutilation are a gruesome link between many of the deaths, and there are fears the actual toll may be much higher, as tens of thousands of people are listed as missing.

These are the main drug cartels at the centre of the bloody turf war, all vying for control of the lucrative smuggling routes between South America and the US.

Gold and silver-plated and diamond-encrusted guns believed to belong to the Sinaloas, seized by police in 2010 ( Mexico Attorney General Office: AFP )

Gulf cartel

The Gulf cartel is perhaps the oldest organised crime group in Mexico and is known for intimidating local civilians and being particularly violent.

Former allies of the Zetas, the Gulf cartel are now believed to be allied to the Sinaloa cartel.

Its founder Juan Guerra - considered to be the "godfather" of the cartel - smuggled alcohol into the US in the 1930s.

After the end of the Prohibition, Guerra, widely known as Don Juan, turned his focus to drug smuggling.

Juan Garcia Abrego is led out of an FBI office after his arrest in 1996. ( Reuters )

In the 1970s the command shifted to Guerra's nephew, Juan Garcia Abrego. He lead the lucrative business until his arrest and extradition to the US in 1996.

After a series of internal battles Osiel Cardenas took over. As his cartel grew, he created Los Zetas, a new armed wing made up of military defectors.

The two groups were collectively known as The Company.

Los Zetas was designed to protect the Gulf from the Sinaloa cartel, but would eventually turn against its creator.

In 2004 Cardenas was arrested. Sensing weakness in the Gulf cartel, rival gang Sinaloa tried to move in on the Gulf stronghold of Nuevo Laredo.

In 2005 hundreds of extra police were sent in to try and quell the conflict, which killed thousands of people.

Among the dead was Manuel Farfan, who stepped into the role of police chief and was fatally shot just hours after he was sworn in.

The Gulf cartel emerged victorious from the battles.

In 2010, Los Zetas and the Gulf split, prompting further bloodshed. This was followed by the arrest of Gulf chief Jorge Eduardo Costilla Sanchez.

Two factions within the cartel are believed to be fighting for full control.

Los Zetas cartel

Los Zetas is one of the largest drug cartels in Mexico, and is known for brutal tactics, including torture and beheading.

On several occasions, the group has strewn the mutilated bodies of its victims on Mexican roads and highways to scare rival gangs, particularly the Sinaloa Federation.

The group takes its name from the radio code used for top-level Mexican army officers.

It was set up in the 1990s by former elite Mexican soldiers, who were then aligned with the Gulf.

Heriberto Lazcano is known as The Executioner ( Reuters )

Among them was Heriberto Lazcano - known as The Executioner - who was the group's leader until October 2012, when he was killed in a gunfight with Mexican marines near the Texas border.

However questions have surrounded his death after his body was snatched from a funeral parlour.

Former second in command, Miguel Trevino Morales, then took charge of the Zetas and was known for his violent and confrontational personality. He was arrested in his home town of Nuevo Laredo on July 14, 2013.

His brother, Omar Treviño Morales, then took up the helm, before his capture earlier this year.

The Zetas are known for carrying out brutal massacres and displaying the corpses of their mutilated victims.

The gang now aligns itself with the Tijuana, Juarez and Beltran-Leyva cartels.

Along with drugs, the Zetas are involved in kidnapping, extortion, assault and racketeering.

Sinaloa cartel

The Mexican army destroys thousands of guns that were seized from drugs cartels ( AFP: Jesus Alcazar )

Once known as the Blood Alliance, the Sinaloa cartel is considered as one of the most powerful organised crime groups in the world and is notorious for its brutality.

In 2010 the ABC's Tim Palmer revealed the Sinaloa syndicate is behind many of the shipments of cocaine to Australia.

A source told Palmer the cartel has had operatives in Australia for several years.

The cartel is associated with the label "Golden Triangle", which refers to the states of Sinaloa, Durango and Chihuahua - regions that produce Mexican opium and marijuana.

It relies on high-level connections and corrupt officials to get the upper hand on rivals. As InSight Crime notes, an official can "double or triple his salary by simply agreeing to look the other way".

It was formed in the 1960s by Pedro Aviles Perez - considered to be the father of large-scale drug trafficking in Mexico and the pioneer of the use of aircraft to smuggle drugs to the US.

He was killed by police during a shootout in 1978.

His nephew, Joaquin Guzman, currently leads the main Sinaloa group from an unknown location.

Nicknamed "El Chapo" or "Shorty", he was jailed in 1993 and escaped in 2001 and resumed control of the cartel.

He was recaptured in 2014 but escaped again in a brazen prison break in July 2015, after he spectacularly broke out of his cell through a 1.5 kilometre tunnel underneath his shower.

He was again recaptured in January 2016, with Mexico's President Enrique Pena Nieto tweeting: "Mission accomplished: We got him. I want to inform Mexicans that Joaquin Guzman Loera has been arrested."

The tunnel emerged at a building site 1.5km away from Altiplano prison ( Reuters: Attorney General Office )