In the underworld, there are always several people wanting a piece of the illegal pie. And they are willing to kill for it. No matter how formidable a criminal faction is, it will always have dangerous enemies. Such was the case for the mother charter of the Sons Of Anarchy Motorcycle Club aka SAMCRO.
While some threats were easy to fend off, others gave Charming's star bikers plenty of headaches. And even though the San Joaquin Sheriff Department mostly worked with the Sons, law enforcement agencies like the ATF were more than eager to see the notorious biker gang go down for good.
SAMBEL
The Sons Of Anarchy Belfast Charter didn't really succeed in any of its plants. SAMBEL was supposed to be working together with SAMCRO. Unfortunately, its president Keith McGee had gotten in bed with IRA member Jimmy O. Before his death, he was planning to run the mother charter out of the gun business so that his own charter would get more revenue.
Though it was planned without his knowledge, SAMBEL was planning to kill the Sons during their Ireland visit by rigging a gun shipment with explosives. After being captured and tortured, McGee's deputy O'Neil revealed that the president was working with Jimmy O. McGee was thus killed by Clay by being pushed off a building.
Mayans
For most of the series, the Mayans were allies rather than enemies, hence they rank lowly in terms of harm caused. At the start of the series, the Mayans were at war with SAMCRO. They had just robbed the club's warehouse and burned it down. This prompted a war over the San Joaquin valley territory.
A truce happened but in the second season, the Mayans aligned themselves with LOAN, who the Sons totally hated. They protected LOAN leader Ethan Zobelle from the Sons and in the end, he managed to escape without getting killed. The Mayans then re-entered into an alliance with SAMCRO.
One-Niners
How much harm did the One-Niners cause SAMCRO? Not much. It was mostly a cold war between the two. Bad blood developed when they attacked a meeting between SAMCRO and the Mayans. Luckily, the Sons escaped. Clay tried to frame the Niners for killing Donna, causing an old and weak Piney to try and seek revenge by himself.
The relationship became better when the Niners helped the Sons wage war against the Aryan Brotherhood. However, the Sons and the Niners took sides in the war between the Galindo Cartel and the Lobos Sonora cartel, forcing them to fight again. Clay later framed the Niners for shooting him, causing Tig to try and kill Laroy but ended up killing Veronica Pope instead.
Russian Mafia
Judging from documentaries, the Russian Mafia is probably more lethal in real-life than in Sons Of Anarchy. In the FX series, it was one of the weaker criminal organizations. Initially, the Russian Mafia was on good terms with the club. They betrayed Jimmy O'Phelan when the Sons offered the $2 million to hand over the man.
Hostility brewed up when they found out that the money they had been given was counterfeit. They targeted Jax but failed to cause any serious bodily harm to harm. The Sons later massacred down a good number of Russian mobsters during Opie's wedding. When the remaining members kidnap Jax and Opie, they were gunned down by Romeo and his Galindo associates.
Lobos Sonora
The Lobos Sonora cartel had an actual battlefield war with the Sons. Together with Romeo and Luis, a few bikers sneaked into a Lobos camp where a full-fledged battle took before. The Lobos had rigged the ground with landmines, causing the death of Kozik. Jax and Chibs then used Rocket Propelled grenades to wipe out most of the Lobos members.
After this war, the cartel disappeared from Charming. Despite being fierce towards other gangs, Lobos Sonora never got close to taking out SAMCRO. The best they ever did was destroy the gate at the Clubhouse premises.
Lin Triads
The relationship between SAMCRO and the Lin Triads was mostly cordial throughout the first five seasons. Things took a turn for the worst when Gemma framed a Triad member for killing Tara. Jax reacted by torturing and killing the suspect, thus kicking off a major war between the two factions.
The avoidable war brought plenty of damage to SAMCRO. Their biggest attack happened when they massacred 16 prostitutes at the Diosa. With help from other gangs such as the Grim Basterds and the One-Niners, SAMCRO won the war and wiped out all the Triads, including their leader Henry Lin.
ATF
Two major ATF agents—Josh Kohn and June Stahl—were responsible for the woes that the club faced. Kohn came to Charming to investigate the Sons but he had a hidden agenda. As Tara's ex, he was in love with her and wanted her back. He kept stalking her and almost sexually assaulted her before Jax put an end to the madness.
Stahl was more menacing. After being beaten by Otto, she became obsessed with taking down the club. She framed Opie and Gemma, kept Bobby in prison longer than he should have been, and kept on targeting various members as soon as she sniffed out weakness. Stahl indirectly caused plenty of destruction, including the death of Donna, hence the ATF's threat is one to acknowledge.
Pope Partners Inc.
Pope Partners, Inc. was responsible for the death of two key SAMCRO members, namely Opie and Bobby. It was also responsible for the death of Tig's daughter. These three separate incidents were some of the saddest moments in the history of the club.
Under the leadership of Damon Pope, and later August Marks, Pope Partners Inc. had invested heavily in the construction industry to mask its real business which was trafficking heroin. The organization also had control over several African American gangs in California, using them to wage war against its enemies.
True IRA
The True IRA provided two of the show's best villains—Jimmy O'Phalen and Galen O'Shay. Family members weren't off-limits for the True IRA. Jimmy had a history with Chibs, having chased him out of the UK and taken his wife and daughter. He also used Abel as bait in his war against the Sons.
Galen, on the other hand, used heavy-handed tactics to try and force the Sons into staying in the gun business. He even murdered two Prospects and mutilated their bodies. He then staged the biggest ever attack against the Sons by blowing up their Clubhouse. Were it not for Jax's keenness, everyone would have died.
LOAN
The League of American Nationalists (LOAN) is the only criminal faction to have a major win against SAMCRO since its leader Ethan Zobelle escaped without getting killed. The white supremacist group brought plenty of havoc to SAMCRO's door.
Zobelle recruited several influential businessmen as well as gangs such as Aryan Brotherhood and used them to wage war against the Sons. He ordered Gemma to be raped and for Bobby to be attacked. He also had Otto attacked in prison. His men then planted a bomb in a van, injuring Chibs. LOAN also burned down Cara Cara, thus affecting the club's income.