Pirate Alliance

A Pirate Alliance is a pact between two or more pirate captains and their respective crews.

Leadership
The captains who formed the alliance are theoretically equal in status, and cannot give each other orders. They may have limited control over each other's crews, but the highest authority still lies with the respective captains.

In a situation where one of the captains gets captured, the other can take charge of their remaining subordinates.

Goals and Benefits
An alliance is usually formed with the purpose of reaching a specific, mutual goal. It may be something that neither crew could accomplish on their own, such as defeating a powerful enemy.

Issues
A common problem with pirate alliances is betrayal; when one captain sees no more use of the other, it results in treason in order to reduce the needs to share glory. Also, due to their mutual goal being the only thing that binds them together, they usually have little to no respect for members of the allied crews, leading to one insulting the other behind their backs or even attacking them over perceived threats.

For Shichibukai, forming an alliance essentially means forfeiting their status, as the World Government does not permit such affiliations with criminals.

Another problem is that an attempt to even establish an alliance between Captains and their respective crews can result in conflict if it fails like when Shiki and his crew tried to forge and alliance with Gol D. Roger and the Roger Pirates which resulted in the Edd War when Roger rejected Shiki's offer of an alliance.

Buggy and Alvida Alliance



 * Status: Active

The Buggy and Alvida Alliance is an alliance formed by the pirate bands known as the Buggy Pirates and the Alvida Pirates (although only its captain remained from them) and led by the leaders of the groups, Captains Buggy and Alvida. They teamed up in order to defeat a common enemy, Monkey D. Luffy, and remain allied even after this failure, to find Captain John's lost treasure. As Buggy has became a Shichibukai during the time-skip, he is forbidden to hold an alliance with Alvida as equals, though no action or knowledge is seen taken against Buggy.

Saruyama Alliance



 * Status: Active

The Saruyama Alliance is an alliance that was formed between three pirate captains, Montblanc Cricket and his surrogate sons "Salvage King" Masira and his brother "Sonar King" Shoujou. It composes of two pirate crews led by the brothers: the Masira Pirates (マシラ海賊団) and Shoujou Pirates (ショウジョウ海賊団). Unlike many other alliances seen, they are extremely loyal to each other to the end, akin to a family. They work together to salvage evidence for the lost Sky Island, in order to prove Cricket's ancestor, Montblanc Noland, was not a liar. Their alliance continued in search for new dreams, and currently looking for the 'Island of Dreams', Nakrowa.

New Fishman and Flying Alliance

 * Status: Disbanded

The New Fishman Pirates and the Flying Pirates, led by Hody Jones and Vander Decken IX formed an alliance in order to overthrow the Ryugu Kingdom. The two conspired to have Hody break into the palace while Decken could capture Shirahoshi and marry her. However, the plan failed, and the alliance did not last very long, with Hody even declaring Decken useless. After Decken sent Noah after Shirahoshi, Hody stabbed him with a trident in order to send Noah down towards Fishman Island, effectively ending their alliance.

Heart and Straw Hat Alliance

 * Status: Active

On Punk Hazard, the Heart Pirates and Straw Hat Pirates, two crews from The Worst Generation, formed an alliance. The respective captains, Trafalgar D. Water Law and Monkey D. Luffy, teamed up with the sole purpose of overthrowing Kaido of the Yonko. This alliance was proposed by Law, who, at the time, was still a Shichibukai.

However, the true reason for the alliance was to destroy the SMILE Factory that belonged to another Shichibukai Donquixote Doflamingo who allied with Kaido; what Law did not inform Luffy at the time was that he intends to kill Doflamingo and destroy the entire Donquixote Pirates to avenge the death of Donquixote Rosinante. The alliance was placed in the newspaper the next day and all around the world people reacted in shock upon learning of it. Kinemon and Momonosuke joined the group hoping to save Kanjuro. During the Dressrosa Arc, Law called off the alliance while facing Doflamingo but after being captured Luffy forced him back into it stating that it was his choice and not Law's, much to Law's irritation, but reluctant acceptance.

As Law is a Shichibukai, he was forbidden from allying with pirates who are not allied with the Government, and as such his title is revoked. Although they have yet to achieve their promised goal of defeating Kaido, the alliance has succeeded Law's desired result of defeating Doflamingo; the results of this alliance were reported at a global scale. This alliance is notable as the two captains of this alliance Monkey D. Luffy & Trafalgar D. Water Law are both carriers of D.

After the events of Dressrosa the alliance is now official. Some victims of birdcage asked Luffy to take them under his wings, but the rubber man refused and the group introduced an underling's vow forming the "Straw Hat Grand Fleet" a huge group of warriors with seven representatives.

Currently the alliance has the following organization:
 * Luffy, Law, Zoro, Usopp, Robin, Franky, Kinemon, and Kanjuro are on Going Luffy-senpai as guest of Barto Club and are currently heading to Zo.
 * The Heart Pirates (except Law) are on Zo waiting for their captain.
 * The Thousand Sunny's group (Sanji, Nami, Chopper, Brook, and Momonosuke) arrived on a mysterious island carrying Caesar Clown as a hostage. They gained information about a strange girl and another samurai.
 * The Tonta Corps returned to Green Bit. The Tontattas are revealed to the citizen of Dressrosa as dwarves (not fairies) and now are in harmony with the humans. They turned Lucy/Luffy and Usoland/Usopp into national heroes.
 * The Beautiful Pirates, the Happo Navy, the XXX Gym Martial Arts Alliance, Hajrudin and the Yonta Maria Grand Fleet are traveling in the world with a piece of Luffy's Vivre Card.

Kid, On Air, and Hawkins Alliance

 * Status: Active

During the Punk Hazard Arc, three captains of The Worst Generation, Eustass Kid, Scratchmen Apoo and Basil Hawkins, met on the Kid Pirates' base to discuss the terms of an alliance for the sole purpose of defeating Shanks. Despite some minor altercations, the three were eventually able to come to terms, and their alliance was reported in the newspaper. After Law and Luffy's victory over Doflamingo, the three pirates were relieved that the two were not going after the same Yonko they were targeting.

Suddenly, Kaido landed on their base and the three found themselves face-to-face with him.

XXX Gym Martial Arts Alliance



 * Status: Active

After the battle on Dressrosa, four of the gladiators who fought in it decided to form an alliance. These were Ideo, Blue Gilly, Abdullah, and Jeet. Ideo was their representative, and the alliance hoped to become subordinates of the Straw Hat Pirates. Although Luffy ultimately rejected, he offered them friendship nevertheless, which they continue to swear their allegiance as the Fourth Division of the Straw Hat Grand Fleet.

One Piece: Pirate Warriors 2
Several alliances are featured in the game One Piece: Pirate Warriors 2 as part game's original story. Though the game is set after the timeskip, Whitebeard and Ace are still alive and Blackbeard is still a member of the Shichibukai. While Sakazuki is Fleet Admiral and Kuzan has left the Marines, Garp is still a Marine Vice Admiral, CP9 is still works for the World Government, and Magellan is still Chief Warden of Impel Down. The story deals with mysterious Frenzy & Control Dials which where being researched by World Government on Punk Hazard. The Straw Hat Pirates come across a Control Dial following an adventure on Skypiea which Luffy decides to keep due to its uniqueness and end up being chased to Punk Hazard while running from Garp and Smoker. Luffy's Control Dial ends up activating the Frenzy Dials stored in a lab on Punk Hazard, causing several members of the Straw Hats and Smoker's G-5 Marines to be corrupted by the Frenzy Dial's madness inducing fog, forcing Luffy, Nami, and Smoker to use the Thousand Sunny to escape from their former allies leading to a bounty being placed on Smoker's head by the Government, forcing Luffy and Nami to form an alliance with him and eventually several other pirates and marines in order to free Luffy's crew and deal with the threat posed by the Frenzy & Control Dials, causing them to come into conflict with various other alliances formed to combat oppression by Marines under Fleet Admiral Sakazuki.

Straw Hat Alliance
After most of Luffy's crew and some of Smoker's G-5 Marines falls under the influence of the Frenzy Dial, Luffy and Nami join forces with Vice Admiral Smoker and his uncorrupted G-5 subordinates after escaping Punk Hazard and a bounty is placed on Smoker's head by the government. They manage to find Franky and restore him back to his senses. They are later joined by Jinbe and his Sun Pirates during a battle with marines lead by Garp & Kizaru. Eventually they manage to find Chopper & Brook on Thriller Bark, and manage to restore them to their senses. After defeating Moriah and Perona, as well as Buggy and Galdino of the Great Pirate Alliance, they are approached by Ace who offers to take them to Whitebeard to talk about forming alliance with Whitebeard. However Luffy gets into an argument with Whitebeard leading to a fight between Luffy's group and the Whitebeard Pirates and they manage to defeat Ace, Jozu, Vista, and Macro which impresses Whitebeard enough to agree to an alliance, resulting in the Straw Hat & Whitebeard Alliance.

Straw Hat & Whitebeard Alliance
An alliance between the crews of pirate captains Luffy and Edward Newgate, formed to combat the threat posed by the Marines and Great Pirate Alliance and to aid Luffy and Smoker in their quest to learn more about the Frenzy dials and help Luffy and his crew (consisting of Nami, Franky, Chopper, and Brook) find their four remaining crewmates, while Whitebeard Pirates gain an ally in combating the Marines lead by Sakazuki and Great Pirate Alliance lead by Buggy. With the Whitebeard Pirates help, they return to Punk Hazard to learn more about the governments research into the dials in the hopes it can lead them to the whereabouts of Luffy's remaining crew, but are confronted by CP9 and Marines lead by Sakazuki. Fortunately, Kuzan arrives to hold off Sakazuki while Nami searches the lab on Punk Hazard but discovers the dials are gone. Kuzan decides to join forces with them and they travel to the governments second Dial research facility in Impel Down. They are later joined by Perona after defeating her while she was working with Crocodile and Arlong Alliance. Boa Hancock joins forces with them to aid Luffy, allowing them to infiltrate Impel Down to learn more about the dials. Eventually they discover that Blackbeard has stolen the Governments research on the Control and Frenzy Dials at Punk Hazard and Impel Down. After they are defeated by Blackbeard and Moriah who defect from the Great Pirate Alliance to form the Blackbeard Alliance, an injured Luffy is saved by Law and after Luffy recovers at Sabaody, Bartholomew Kuma joins the alliance to combat the new threat posed by the Blackbeard Alliance. Dracule Mihawk later decides to defect from the Blackbeard Alliance to join them as well, while Vista falls under Blackbeard's control. Crocodile joins after he and his forces are rescued from the corrupted Nico Robin and CP9 agents under Blackbeard's control, during which time Galdino is freed from Blackbeard's influence. Emporio Ivankov of the Revolutionary Army joins to assist Luffy and the Alliance in defeating the Blackbeard Alliance. Eventually they manage to free Nico Robin and Usopp at Moriah's base on Thriller Bark, though Moriah escapes with the help of Zoro and Sanji. Eventually Buggy and several escaped Impel Down prisoners join as well during a confrontation with Magellan, while Vista is freed as well. During the attack on Blackbeard's base in Enies Lobby, Zoro and Sanji are freed and the Straw Hat Pirates are reunited, though the Alliance between them and the Whitebeard Pirates continues due to the threat posed by Blackbeard and the Dials. Eventually they manage to help save marines lead by Garp and Kizaru from Enel and the government calls for a temporary truce with the Straw Hat/Whitebeard Alliance and retracts the bounty on Smoker's head. As a result Garp decides to work with the alliance along Smoker to combat the Blackbeard Alliance. However an attempt at an official alliance between them and the Marine's dissolves due to a breakdown in talks between Sakazuki and Ace. Blackbeard manages to take control of Whitebeard which leads to two different possible endings:

If Whitebeard dies, Blackbeard steals the Gura Gura no Mi, causing the Straw Hats and Whitebeard Alliance to join forces with the Marine after Sakazuki is ordered to by the government, resulting in an epic final battle on Punk Hazard resulting in Blackbeard's defeat at the hands of the Straw Hat Pirates. Following Blackbeard's defeat, alliance disbands with the Straw Hat Pirates parting ways with the Whitebeard Pirates lead by Ace who becomes Captain of the Whitebeard Pirates in the wake of Whitebeard's death.

If Whitebeard lives, Law officially joins the alliance to combat the corrupted Teach and his corrupted followers. Working with the Alliance, Smoker and Garp gather the remaining uncorrupted Marine forces to maintain public order while the Whitebeard Pirates continue to defend their territories from attack by the Blackbeard Alliance. Law and the Straw Hats eventually figure out that the Blackbeard Alliance is being supplied with Frenzy Dials from the Sky Islands and they travel their to put an end to it, only to be confronted by Kizaru and Enel. Eventually they manage to return Kizaru and Enel back to their senses, causing them to join the Straw Hat/Whitebeard Alliance in the final battle on Punk Hazard against the corrupted Blackbeard, Moriah, and Sakazuki. They are assisted by Bentham who uses his Mane Mane no Mi to disguise himself as Whitebeard to divert the attention of the Blackbeard Alliance away from the real Whitebeard, who inspires Kizaru, Kuzan, Enel, and Luffy during the final battle against Moriah, Sakazuki, and Blackbeard. Law protects Luffy from Blackbeard's attack, and Smoker manages to briefly pin Blackbeard with his Nanashaku Jitte before eventually brakes, giving Luffy enough time to prepare a Gomu Gomu no Elephant Gatling/Grizzly Magnum combo which he uses to defeat Blackbeard, destroying the Control Dial in Blackbeard's possession. After Blackbeard is defeated by Luffy, the alliance disbands and the Straw Hats continue on their journey after parting ways with Law and the Whitebeard Pirates.

Great Pirate Alliance
Using his status as a former member of the Roger Pirates, Buggy forms an Alliance between several pirates and criminals (Krieg, Wapol, Galdino, etc.) to combat the Marine oppression under Fleet Admiral Sakazuki. After the break up of the Straw Hats due to the Frenzy Dials and a bounty is placed on Vice Admiral Smoker's head by the government, Buggy makes a secret pact with the World Government to capture the Straw Hat Alliance and hand over the Control Dial possessed by Luffy. The Great Pirate Alliance becomes strong enough to pose a threat to the Yonko Whitebeard and his crew, resulting in them forming an alliance with Straw Hats in response. Eventually Buggy realize his forces are strong enough to challenge the Marines and decides to raid Marineford resulting in a three way battle between them, the Marines, and Staw Hat and Whitebeard Alliance. However Blackbeard and Moriah defect from them after learning about the Frenzy and Control Dials, which they use to corrupt marines, pirates, and government personal. After the Battle at Marineford and the rise of the Blackbeard Alliance, the Great Pirate Alliance dissolves with Galdino, Wapol, and Krieg being corrupted to serve Blackbeard. Galdino is later freed from Blackbeard's control and Buggy manages to avoid falling under Blackbeard's control and briefly tries to rebuild it with the aid of some Impel Down prisoners who idolize him, but after losing to the Straw Hat and Whitebeard Alliance, Buggy decides to join forces with them to combat Blackbeard Alliance.

Crocodile and Arlong Alliance
A loose alliance formed between Crocodile and Arlong Pirates to avoid joining Buggy's Great Pirate Alliance. Perona ends up joining them after separating from Moriah following their defeat by the Straw Hat Alliance at Thriller Bark. With the aid of Crocodile, Arlong rebuilds Arlong Park which they use as their alliances main base. However Perona defects to the Straw Hat/Whitebeard Alliance after being defeated by them and Hatchan is convinced to leave the Arlong Pirates due to his friendship with the Straw Hats. The Alliance between Arlong and Crocodile is very weak due to Crocodile habit of manipulating Arlong and his crew, as well as Arlong's views of fishmen being racially superior to humans. They are eventually defeated by the Straw Hat/Whitebeard Alliance and dissolve. Perona and later Crocodile end up joining forces with the Straw Hat/Whitebeard Alliance, while Arlong and Hatchan fall under Blackbeard's control, though Hatchan is later freed and Arlong is defeated along with Blackbeard.

Blackbeard Alliance
The main antagonist faction in the game which was formed by Marshall D. Teach, Gekko Moriah, and Enel after learning of the Control Dial's ability to control people under the effects of the Frenzy Dial. With help from Moriah, Blackbeard managed to steal the Control Dial from Luffy, severely injuring him in the process. By using the Frenzy Dials to corrupt various people and while others to joined out of either fear or the threat of being controlled. The Blackbeard Alliance managed to corrupt powerful individuals like CP9, Impel Down staff, Galdino, Bentham, Hatchan, Vista, Krieg, and Arlong. Blackbeard also managed to bring the four remaining corrupted Straw Hats (Robin, Usopp, Sanji, and Zoro) under his control as well though most of them are eventually freed by the Straw Hat/Whitebeard Alliance. Due to the threat he posed thanks to his possession of the Control Dial, Blackbeard and his Alliance become enemies of both the Straw Hat/Whitebeard Alliance and the Marines, to the point the Government declares a temporary truce, though Sakazuki unwillingness to work with them foils any real possibility of an alliance between the two, which Blackbeard takes advantage of to corrupt Whitebeard.

If Whitebeard dies, Blackbeard steals the Gura Gura no Mi and due to the threat he poses Sakazuki is ordered by the Government to work with the Straw Hat/Whitebeard Alliance, though his desire to take the Control Dial from Blackbeard ends up working in Blackbeard's favor during the final battle. Usopp and Franky build an Anti-Control Dial device as a way to nullify the effects of Blackbeard's control dial. Blackbeard eventually turns on his allies and uses the control dial to brainwash Moriah and Enel, only to be defeated in the end by the Straw Hat Pirates.

If Whitebeard lives, Blackbeard uses the control dial on its maximum setting, but loses control of his brainwashed forces and the corrupting fog of the Frenzy Dial fuses with the darkness of Blackbeard's Yami Yami no Mi causing Blackbeard to be corrupted. The corrupted Blackbeard uses his black holes to capture and corrupt Kizaru, Sakazuki, Enel, and Moriah indiscriminately attacking various regions and bolstering their forces with Frenzy Dial provided by Enel from the Sky Islands. Eventually Enel and Kizaru are freed causing them to join the Straw Hat/Whitebeard Alliance and Blackbeard's supply of Frenzy Dials is cut off, resulting in an final showdown on darkness corrupted Punk Hazard. Sakazuki, Moriah, and Blackbeard are defeated putting an end to the threat of both the Frenzy Dials and the Blackbeard Alliance.

Trivia

 * The World Government fears that if at least two Yonko ally together, they could cause an upset in balance.
 * Interestingly, Buggy urged his captain Gol D. Roger to accept an alliance with Shiki though his cries fell on deaf ears as his Captain enjoyed his freedom too much to consider an alliance. Years later as a Pirate Captain himself, Buggy would strike up an alliance with Alvida, meaning that in contrast to his former captain, Buggy seems to favor alliances between crews (especially if they have a common enemy).