Obviously as one gets more in depth in reading the arcs in One Piece, one would discover the themes are really drawn from some works of literature, some literary genres and even some Characters are inspired by literature. For example the horror genre was explored in the thriller bark arc, with inspirations, as I can spot from Frankenstein and Strange Case of Dr Jekyll and Mr Hyde. Other mythical creatures seem to inspire Oda further in the current arc but as we saw mermaids were already a folk creature that we saw previously. The Alabasta arc had some similarity with 1001 Nights. Sky island was certainly influenced as well by the flying island in Gulliver's travels. Impel Down was influnced by Dante Alighieri's Inferno Just something off the top of my head, please remind me of more as there have been more.
The Ancient Kingdom was overthrown by what is know as the world government. ( Vol. 51 Chapter 497 and Episode 391, Pappug tells to the Straw Hats when and how the World Government was founded.) The World Nobles are thus named the creators of the world. 五老星 Gorōsei the “behind the scenes” leaders.
For some reason Wiki tells you to look into Sparta as the link to Gorosei but as I understand it Oda is critquing Japanese elitism. So with minimal search I came up with this.
genrō (元老) - unofficial term for retired Japanese statesmen considered "founding fathers" of modern Japan who served as informal advisors to the emperor during the Meiji and Taisho periods. Experienced leaders of the Meiji Restoration were singled out by the Emperor as genkun, and asked to act as Imperial advisors. With the exception of Saionji Kinmochi, all the genrō were from medium or lower ranking samurai families, four each from Satsuma and Chōshū, the two former domains that had been instrumental in the overthrow of the former Tokugawa shogunate in the Boshin War of the Meiji Restoration of 1867-1868. The genrō had the right to select and nominate Prime Ministers to the Emperor for approval. The first seven genrō were all formerly members of the Sangi (Imperial Council) which was abolished in 1885. They are also sometimes known to historians as the Meiji oligarchy, although not all of the Meiji oligarchs were genrō. Historians would be directly related to the Gorosei in OP universe also they are Imperial advisors like the genro were in Japan.
I think this is a nice quote that underlies the similarities of the revolution in Japan vs the revolution in One Piece “The Emperor of Japan announces to the sovereigns of all foreign countries and to their subjects that permission has been granted to the Shogun Tokugawa Yoshinobu to return the governing power in accordance with his own request. We shall henceforward exercise supreme authority in all the internal and external affairs of the country. Consequently the title of Emperor must be substituted for that of Taikun, in which the treaties have been made. Officers are being appointed by us to the conduct of foreign affairs. It is desirable that the representatives of the treaty powers recognize this announcement.”
—January 3, 1869 Mutsuhito,
It should also be noted that the Meiji Restoration created military rule over the land which is exactly like one piece. "Enrich the country, strengthen the military" (富国強兵 fukoku kyōhei?) In OP the Void Century is created because the WG was so powerfull which also shows the Gorosei contoling history again like the Japanese Genro. The class system during this time in Japan was strengthened...Poor be poor-rich be rich. "Emperor is the head of the Empire, combining in himself the rights of sovereignty". This is much like in One Piece where we see a few elites leading a massive world. The Genro remained the inner circle elites that helped dictate what the Emperor could do. The Genro are much like the Gorosei in One Peace and the Emperor would be somewhat similar to the Fleet Admiral. One last thing: The genrō had the right to select and nominate Prime Ministers to the Emperor for approval. Prime ministers in One Piece would be similar to Shichibukai. (七武海 Shichibukai?, literally meaning "Seven Military Seas"), the full title being Oka Shichibukai (王下七武海 Ōka Shichibukai?, literally meaning "Royal Seven Military Seas") Genro as noted earlier was a group of seven samurai.
I just want to point out one last thing about Japanese history and a possible connection to OP Sengoku period (戦国時代, sengoku jidai) was a time of social upheaval and nearly constant military conflict that lasted roughly from the middle of the 15th century to the beginning of the 17th century. gekokujō (下克上?), which literally means "the underling conquers the overlord."...You can take your own interpretation. I’ll just point out a couple things: 1) Under Sengoku in OP the world was in constant war much like Sengoku period in Japan. Also when Sengoku is first introduced on http://www.mangareader.net/103-2341-...apter-234.html it states “Together means war country” 2) You should read about gekokujo but essentially the weak took over the strong which would resemble the WG in OP taking over the Ancient Kingdom.
In mythology: 'The Wealthy One,' as is the Greek Plouton. This is because everything is born of the earth and returns to it again." Not a connection but maybe in the future? (IDK). The best thing I could find was The Orphic Hymn to Pluto addresses the god as "strong-spirited" and the "All-Receiver" who commands death and is the master of mortals. It was also said that Pluto was a “hidden” god. “Come forth Plouton.” As we know Pluton, in OP, is hidden. One really interesting fact is that Pluto had a helmet (kyneê) which gave him the ability to be invisible. Later on translations called it: "helmet of Orcus" referring to those who conceal their true nature by a cunning device. Francis Bacon said, "the helmet of Pluto, which maketh the politic man go invisible, is secrecy in the counsel, and celerity in the execution." I believe Franky made Plouton and they are currently traveling on it...hidden in plain sight.
Poseidon is: Weakoshi who has the capability of calling forth extremely large sea kings to do her bidding. These sea kings are capable of sinking Islands. Poseidon in mythology was known as: “Earth Shacker.” Before the Trojan War Poseidon sent a sea monster to attack Troy. The monster was later killed by Heracles. In Greek art, Poseidon rides a chariot that was pulled by a hippocampus or by horses that could ride on the sea. He was associated with dolphins and three-prongedfish spears (tridents). He lived in a palace on the ocean floor, made of coral and gems. This is interesting as Weakoshi is going to be carried by Sea Kings on Noah. Noah being reference to Bibilical parable, where Noah carried two of every animal aboard a ship.
The Jaya and Eldorade arc is influenced by a Pirate story by E A Poe - that one is certain.
a couple of hypothetical:
Gargantua - The main caracter is a very hungry and fat giant, and the later half of the book depicts a war fought over sweet bread. - Big Mam?
Argonatica - a ancient greek play that contains sirens (mermaids), harpies and a dragon and a form of pirates in the form of Jason and his men that travels the seas on Argo. Punk Hazard?
Mostly all of his characters that he makes that are part of the main story are from real life pirates that have been around too. The only difference is that he mixes and matches there names around so that it's not like he's copying anyone... I mean if you look at blackbeard and whitebeard. In the real world, blackbeard real name was Edward Teach, yet in the manga he gave the name Edward to whitebeard instead and kept Teach for blackbeard. It's actually fun to see what else he has done to others names.