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 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.

Problems
A common problem with Pirate Alliances is betrayal.

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

Buggy and Alvida Alliance
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.

Saruyama Alliance
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).

Hody and Decken Alliance
Hody and Decken forms an alliance to overthrow the kingdom. Hody's job was to invade the castle while Decken backs him up to capture Shirahoshi. The alliance did not last very long, when Decken later attempt to control the Noah to, Hody decided to stab him to release his power down to Fishman Island.

Heart and Straw Hat Alliance
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 throwing Kaido of the Yonko. However, the true reason for the Alliance was to destroy the SMILE Factory that belonged to the Shichibukai Donquixote Doflamingo who allied with Kaido. The alliance was placed in the newspaper the next day and all around the world people reacted in shock upon learning of it. During the Dressrosa Arc, Law called off the alliance while facing Doflamingo but after being captured luffy forced him back into it stating it was his choice not law's.

Kid, On Air and Hawkins Alliance
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 an unnamed Yonko. Despite some minor altercations, the three were eventually able to come terms as their alliance was placed in the newspaper.