Prison Gangs are criminal groups which operate inside prisons.
Prison gangs can be either gangs whose foundation was inside a prison or established by incarcerated members of a specific criminal organization. Traditionally, a prison gang is one which was first born inside prison and whose primary agenda is to achieve power within the penal system and it's primary enemy is other prison gangs and/or the prison authorities (though the more ambitious prison gangs end up expanding their influence to the outside world).
Prison gangs which are established inside prison by incarcerated members of external groups are usually focused on protecting their incarcerated members, providing for them while inside, and making sure that they continue to remain loyal to the organization. Some of the prison gangs (e.g. Mexican Mafia) evolved into organized crime syndicates. Such as the West Virginia Gang (ROS) Rise Of Success.
It was in the latter part of the 20th century, that the prison gang was born. The earliest were formed in California in the 1950s, which were black and white prison gangs that were in opposition toward each other and preyed on the other ethnic groups (e.g. Latinos). Eventually, the first of the national prison gangs was founded in a California prison which was the Mexican Mafia. It was established in 1957 in response to the predations of the white and black prison gangs on the Latino inmate population. The Mexican Mafia soon proved to be the most ruthless gang of them all and to break up the gang, the prison authorities sent its members to other prisons within the California Department of Corrections. Which simply spread the gang throughout the system, where they soon proved themselves as the most brutal of all the gangs. Soon other prison gangs (Latino, white, and black) were established or became more organized and more brutal in response to the arrival of the Mexican Mafia.
By the racially, socially, and politically turbulent 1960s-1970s, gang wars and race riots were a common feature in many prison systems of the United States (California, the Southwest, the Midwest, and the Northeast). Along with that came an explosion in the drug trade, especially heroin. Factors which contributed to the rise and spread of prison gangs throughout the prison systems of the United States, especially in California and Illinois. These prison gangs soon dominated the prisons, becoming a virtual parallel government in the prison system, one which governed its inmates and whose rule was divided along racial and ethnic lines. They supported themselves by running criminal rackets behind the walls. Into the prisons they smuggled contraband (mostly drugs) and inside they distributed and sold drugs, taxed criminal activity, operated protection rackets on inmates, controlled the markets for contraband (e.g. cigarettes), operated illegal gambling (e.g. sports betting), and controlled prostitution (homosexual). The biggest money maker was heroin and the wars to control that racket were fierce.
It wasn't long before the main prison gangs started to expand their operations to the streets. They started with bank robberies, burglaries, small-time drug dealing, and robbing drug dealers. Soon they progressed to loansharking and heroin trafficking. By the 1970s, the major prison gangs of California (Mexican Mafia, Nuestra Familia, Black Guerrilla Family, and Aryan Brotherhood) had along with the Mexicans displaced the Italian Mafia as the dominant heroin traffickers in the state of California and by that time they had become organized crime syndicates. During the 1970s-80s, the "Big Four" of California had spread to the Federal Bureau of Prisons and become major players within that system. By the 1980s, Texas had become a stronghold of Latino and white prison gangs which had emerged in its prison systems, and so had New Mexico and Arizona.
They too ended up following the lead of the California prison gangs and spread their activities to the streets, especially in drug trafficking and soon the Italians were likewise displaced as the primary heroin traffickers in Texas by the prison gangs and Mexicans. By the 1990s, the Latino prison gangs were organizing Latino street gangs in California, Texas, Arizona, and New Mexico. They were establishing protection rackets on the streets, taxing the gangs, establishing nationwide drug distribution networks (in partnership with Mexican drug syndicates), and using the street gangs as soldiers. A few prison gangs (Texas Syndicate, Mexikanemi, Sindicato Nuevo Mexico, Barrio Azteca, New Mexican Mafia, and the Aryan Brotherhood of Texas) had joined the "Big Four" of California as organized crime syndicates. These nationwide and regional prison gangs established drug trafficking and distribution networks and challenged the power of the Italian Mafia. Working with the Mexican drug cartels they facilitated the smuggling of wholesale quantities of cocaine, methamphetamine, heroin, and marijuana on a weekly basis. Distributed those drugs across the West Coast and Southwest, and through street gangs the Latino prison gangs controlled had those drugs sold on the streets. They also worked as hitmen and enforcers for the cartels. 
Prison gangs continue to exist in the Sixth World. At least one of the nationwide prison gangs of the Fifth World, the Mexican Mafia (aka, La Eme), survived into the Sixth World and as of 2072 was still active and considered to be an ethnic mafia. Two of the prison gangs within the successor states of the former United States have been established by foreign street gangs, Cocotona from Aztlan in the UCAS, the PCC and the CAS and the Yardies from the United Kingdom in the UCAS. The two extremist organizations, Humanis and the Sons of Sauron have likewise established prison gangs within the penal systems of the former United States. Among the gangs, a number of them have formed prison gangs inside the prisons including the Ancients (Seattle), Halloweeners (Seattle), and Chulos (Seattle).
Major organized crime groups have likewise established prison gangs in North America, the Mafia on the East Coast and both the Triads and Yakuza on the West Coast. Like the prison gangs of the Fifth World, they are formed for self-protection against other gangs, ethnic groups, or races (metatypes), to control various criminal activities inside prison, and so on. In other countries elsewhere in the world prison gangs also exist. One such prison gang, the Numbers Gang of Azania is actually a prison gang from the Fifth World, specifically the former nation of South Africa. In the prison systems of some countries, organized crime syndicates like the Vory, Yakuza, Triads, and Ghost Cartels simply control the prisons of their home country due to their near complete domination of the underworld in those nations.
When it comes to prison gangs, especially for those whose objective is money and power, control of the criminal enterprises within the prison walls are of paramount importance. Whoever controls the rackets inside prison, controls the prison itself. Whoever controls the prison, has influence on the streets. Prison gangs earn money from drug sales, loansharking, gambling, contraband, and homosexual prostitution.
In the early 21st century, gambling behind the walls consisted of poker games, sports betting, and gambling pools which were controlled by gangs or their associates. The bookmaking operations were called "tickets" and had consisted of a bookie and his runners. Information on sports was provided by contacts on the outside via the telephone or the monitored electronic system (e.g. email). Though gambling was illegal, to keep the inmates calm and therefore reduce violence the authorities usually did not interfere. Operations that could generate $100s per poker table or $1000s per bookmaking operation every month. Football were the most popular when it came to sports betting.
Within the big houses, homosexual prostitution was controlled by gangs or their associations. Male prostitutes owned by gangs were "rented" out for a fee, sold to other gangs or someone wanting a "wife", and traded between gangs. Some inmates became prostitutes because they were unable to financially pay off their debts and were unwilling to commit illegal acts for a gang to pay off said debt where one group. Other inmates where prostitutes because they were gay and were forced to become sex slaves or they were straight men who had been raped and therefore feminized in the eyes of the inmate population, and become chattel. 
In many prisons around the world, tattoos are a common site among the inmates. The tattoo may be the name or image of a loved one. It can be a religious one, honoring your faith or as a kind of talisman to protect you. The tattoo may political or ideological in nature, making a statement about a cause. It can represent the gang, brotherhood, or society to which you have pledged your allegiance. The tattoo may be one that tells other inmates what is your skill or the reason you have been incarcerated. It can be something as simple as a word to tell the world how you feel or what you think of the guards.
White Power Tattoos
List of some of the tattoos that were used by white prisoners in the former United States (not including those used by specific prison gangs).
- Swastika = It's a religious icon and geometrical symbol used by many cultures in various forms that was "borrowed" by the Third Reich and ever since has been tainted due to it's association with them. White supremacist groups continue to use it as one of their symbols.
- 88 = Numbers representing the letters "H" and "H" as in "Heil Hitler" used by white supremacists.
- Sowilo rune = It's an Armanen rune that looks somewhat like a lightning bolt, which the infamous Schutzstaffel (aka, stormtroopers) of the Third Reich used in their insignia in the form of two of the runes which represent "SS". Which various white supremacist have continued to use since.
- 14 = The number of words in a quote by the Neo-Nazi leader David Lane which is used by white supremacists.
List of some of the tattoos that were used by latino prisoners in the former United States (not including those used by specific prison gangs).
- Sur = It's short for "Sureños", meaning one is a member of the Sureño Nation of gangs that are affiliated with the Mexican Mafia. It is also an abbreviation of Southern United Raza. Sometimes the tattoo is spelled out, Sureño. Those who have the tattoo are known as Sureños or Southsiders.
- 13 = The number 13 represents the letter "M", as in the Mexican Mafia to whom they have pledged their allegiance. The tattoos are also done as X3 and XIII.
- 3-dots = Placed on the hand (usually the fold of skin between the thumb and index finger) or below one of the eyes. Whose meaning is "Mi Vida Loca" (My Crazy Life) and also the hospital, prison, and the cemetery (where the crazy life is likely to take you).
- Norte = It's short for "Norteños", meaning one is a member of the Norteño Nation of gangs that are affiliated with the Nuestra Familia and in opposition to the Mexican Mafia and the Sureños. It may be spelled out completely, Norteño. The Chulos are a Norteño gang, and may sport such tattoos.
- 14 = The number 14 represents the letter "N", as in the Nuestra Familia to whom they pledge their allegiance. The tattoos are also done as X4 and XIV.
List of tattoos that in the former United States were used by all races and ethnic groups.
- Teardrop = It's traditional meaning is that you have committed murder. Over time others have used the tattoo and variations of it to represent that they've lost a loved one while incarcerated or that they were violated in prison (with the rapist putting that tattoo on them as marking his territory).
- Spiderweb = Represents that you have been in prison a long time. Usually placed at the elbows or on your neck.
- Barbed Wire = The spikes represent the number of years of incarceration.
- Love/Hate = On the knuckles of both hands, which were made popular by the 1950s movie, "The Night of the Hunter".
- Rock/Roll = On the knuckles of both hands, as in rock 'n' roll music.
- Stay/Down = On the knuckles of both hands, as in stay down or get a beating.
- EWMN = On the knuckles, and means Evil, Wicked, Mean, Nasty.
- Shiv = Made from something that is already sharp. Like a razor blade that has been attached into the handle of a toothbrush by heating the blade and melting the plastic around the blade.
- Knuckleduster = Usually made from a metal bar or shaped plastic, which may have spikes or some type of protrusions. Handle may or may not be padded.
- Shank = Usually made from a small piece of spring steel taken from the arch of a shoe or leather boot, and sharpened on rock or concrete. In some cases even plastic bags or toilet paper have been melted or glued and shaped into shanks.
- Bone Crusher = Long, stabbing weapon that is made of aluminum, soft iron, or other metals that is shaped and sharpened. Called a bone crusher because it can crack a bone when thrust into the body.
- Spear = Usually it's a metal blade that is tied to a pole made of magazines that have been tightly bound. Normally thrown at someone in another cell.
- Blowgun = Pipe made of magazines or other material, that is used to fire darts. Usually used against someone in another cell.
- Melted chocolate / boiling sugar water = Scalds the target and the sugar/chocolate sticks like napalm resulting in severe burns.
- Soapsock = Sock with a bar of soap inside or in some cases even a pillow case filled with bars of soap (not for gang wars or hits, but for beatings).
- Body Armor = Made from layers of paper turned into a vest or at minimum wrapped around the abdomen. If possible the hardcovers of books. As in the ones from the prison library.
Prison Gangs in the Real 21st Century
Organized crime in California, Arizona, New Mexico, and Texas is currently dominated by Latino prison gangs. They control the Latino street gangs who make up the majority of gangs in those states and therefore control armies on the streets consisting of 1000s or 10s of thousands depending on the prison gang. Specifically in southern California (the Mexican Mafia), Sacramento Valley (Nuestra Familia), Phoenix-Tucson (New Mexican Mafia), Albuquerque (New Mexico Syndicate), El Paso (Barrio Azteca), San Antonio (Mexikanemi), Austin (Texas Syndicate), and south Texas (Mexikanemi, Texas Syndicate, Hermanos Pistoleros Latinos, & La Raza Unida).
These prison gangs have formed alliances with the Mexican drug cartels (Mexican Mafia and Barrio Azteca) or work for them. All of them facilitate the smuggling of drugs into the United States and assist them as enforcers, hit men, and debt collectors on the American side of the border. One of them, Barrio Azteca is deeply involved in the cartel wars in Mexico, being one of the combatants in Ciudad Juarez. The Mexican Mafia is so powerful it even taxes Mexican drug trafficking organizations operating in southern California.
The three main Aryan Brotherhood prison gangs (California, Arizona, and Texas) have also been working for the cartels but since they lack armies of 1000s on the streets, they have nowhere near the power of the Chicano prison gangs on either the streets of the border states or in the drug trade itself. All of the aforementioned Chicano and white prison gangs are involved in the distribution of drugs to other parts of the country, especially the Mexican Mafia which has the most extensive network due to the army it controls of 40,000 to 100,000 gang bangers. The prison systems of California, Texas, New Mexico, and Arizona are dominated by the Chicano / Latino prison gangs. 
Prison Gangs (Research)
- Wikipedia:Prison Gangs (United States)
- Wikipedia:Mexican Mafia
- Wikipedia:Nuestra Familia
- Wikipedia:Texas Syndicate
- Wikipedia:Barrio Azteca
- Wikipedia:Aryan Brotherhood
- Wikipedia:Nazi Lowriders
- Wikipedia:Aryan Brotherhood of Texas
- Wikipedia:Black Guerrilla Family
- History Channel: Gangland, Season 1 Episode 0, Aryan Brotherhood
- History Channel: Gangland, Season 1 Episode 3, Code of Conduct (Mexican Mafia)
- History Channel: Gangland, Season 1 Episode 10, Blood In, Blood Out (Nuestra Familia)
- History Channel: Gangland, Season 2 Episode 4, Texas Terror (Texas Syndicate)
- History Channel: Gangland, Season 4 Episode 7, Aryan Terror (Aryan Brotherhood of Texas)
- History Channel: Gangland, Seasono 5 Episode 4, Blood River (Barrio Azteca)
- History Channel: Gangland, Season 6 Episode 13, Hell House (Sindicato Nuevo Mexico)
- History Channel: Gangland, Season 7 Episode 12, Valley of Death (New Mexican Mafia)