Underworld

The Underworld is the whole system of connections, smuggling and actions which eludes the World Government's control. It is mainly set in the New World.

Organization
According to Law, the New World is divided into territories governed by the strongest pirates thanks to their brokers, pretty similar to a huge crime syndicate. The most influential man in this world is Donquixote Doflamingo, codenamed "Joker".

Due to this nature, the underworld involves almost all the world main forces and strongest men:


 * Yonko: as the most powerful pirates of the New World, they are involved in the Underworld.
 * Kaido is revealed to be Joker's main customer, via the Smiles smuggling.
 * Charlotte Linlin is revealed to be interested in Caesar Clown's Shinokuni weapon as a customer.
 * Supernovas: as formidable New World pirates, some of them has been involved in the Underworld.
 * Trafalgar Law, in order to dethrone Doflamingo and defeat Kaido, acted as Caesar Clown's affiliate. Furthermore, his actions led to the resignation of Doflamingo from the Shichibukai (later revealed as fake news).
 * Kid and Killer, despite not being brokers, watch Caesar Clown's presentation of Shinokuni's power.
 * Shichibukai: some Shichibukai are or were involved in the Underworld.
 * Donquixote Doflamingo is the most influential man of the Underworld under his alias of Joker.
 * Crocodile, as Baroque Works president, was involved in Dance Powder smuggling as a customer.
 * World Government: due to the World Nobles' involvement, the World Government cannot take action against the Slavery.
 * World Nobles are interested in the slave trade.
 * Donquixote Doflamingo was a World Noble.
 * Marines: some former Marines got involved in the Underworld after their dismissal or resignation.
 * Vice Admiral Vergo, as Joker's mole, acted to hide Caesar Clown's illegal actions.
 * Former Scientist Caesar Clown, after the four years ago accident on Punk Hazard, has been involved in the illegal weapons trafficking.
 * Former Admiral Kuzan, after resigning from the Marines, could be involved in the Underworld, as Donquixote Doflamingo and Smoker have speculated.
 * Fishman Island's bloody past is due to slavery.
 * Two peaceful countries are interested in Shinokuni.
 * The Franky Family previously participated in St. Poplar's black market as both sellers and customers.
 * Former Roger Pirates Vice Captain Silvers Rayleigh tried to sell himself as a slave in the Sabaody Archipelago's Human Auctioning House to steal money to pay off his gambling debts.
 * The brothers Kelly Funk and Bobby Funk are renowned hitmen of the Underworld.
 * Suleiman is a renowned killer of the Underworld.
 * The non-canon pirate Breed is affiliated with the Underworld and has been able to got a Smile.
 * Several yet unnamed brokers (at least eleven) are shown watching Caesar's broadcast.
 * An unidentified Jack has affiliations with the brokers and has been notified about Caesar Clown's defeat.

Smuggling
One of the main scopes where the Underworld acts is the smuggling via brokers. This involves illegal goods, rare goods, slaves and illegal weapons.

Past
No tracks about the existence of the Underworld before Donquixote Doflamingo's rise has been revealed so far. However, the tragic past of Fishman Island's slavery is at least 24-years old. It's not clear if this was alright involved in the Underworld.

Several years ago, Boa Hancock, Boa Sandersonia and Boa Marigold got sold as slaves.

In the last ten years, Donquixote Doflamingo built up his status as the most influential man in the Underworld under his alias of Joker. Due to this, in the last four years, he offered Caesar Clown his protection from World Government.

The Franky Family often sold the products of ships dismantling in the black market.

Three years before the start of the series, Crocodile obtained the Dance Powder via smuggling.

Baroque Works Saga
Crocodile's Dance Powder will cause the Alubarna's civil war. When the World Government discovered it, it deprived Crocodile of his Shichibukai status and jailed him in Impel Down's Level 6.

Water 7 Arc
Franky claims to have bought the rare Adam Wood in the St. Poplar's black market.

Sabaody Archipelago Arc
Before reaching the Sabaody Archipelago, the Straw Hat Pirates defeated Duval's Flying Fish Riders, one of the best kidnapping groups and slaves supplier of Disco's Human Auctioning House.

During the Straw Hat Pirates' visit to the Sabaody Park the Hound Pets captured Keimi and sold her to Disco. This causes Luffy's rage, his attack to the Auctioning House and the whole Roswald's Incident. Due to this, Doflamingo forsaked Disco and gave him the entire House.

During the Timeskip
Due to Doflamingo's abandonment and the raid caused by the Straw Hat Pirates, the Human Auctioning House failed and its owner Disco became a vagrant.

Punk Hazard Arc
During Caesar Clown's broadcast for the selling of Shinokuni, the Straw Hat Pirates, Trafalgar Law and Smoker's G-5 act for defeat him, in order to deprive Doflamingo of his supplier of SAD, the main ingredient for the Smiles production.

The defeat and kidnapping of the scientist caused a riot in the Underworld and characters as the Yonko Charlotte Linlin and the unknown Jack were informed about it. Later, Law blackmails Doflamingo, who is forced to resign from his Shichibukai position in exchange for Caesar's return and not become a target of Kaido's fury.

Trivia

 * Both Donquixote Doflamingo and Smoker insinuate that Kuzan may have dealings in the Underworld, though Kuzan neither confirms or denies this.