The Three Great Powers consisting of the Marine Headquarters, the Seven Warlords of the Sea, and the Four Emperors were the three greatest military forces on the oceans. The balance between them is what maintained world peace. They were first hinted to by Yosaku when explaining how Jinbe unleashed Arlong in the East Blue to Luffy and Sanji.
The Three Great Powers originally consisted of the Four Emperors (四皇 Yonkō?), the four most powerful pirate captains in the entire world and their respective crews; the Seven Warlords of the Sea (王下七武海 Ōka Shichibukai?), seven incredibly powerful pirate captains that agreed to become allies of the World Government in exchange for a pardon for past and future crimes; and the Marines (海軍 Kaigun?), more specifically Marine Headquarters (海軍本部 Kaigun Honbu?), where the most combat capable Marines in the world, such as the Admirals, are stationed. With the Seven Warlords working together with the Marines, the government was able to maintain a balance of power with the Emperors.
The Five Elders fear that if this balance gets disrupted, the world itself could descend into anarchy. Furthermore, the balance of power was incredibly delicate; if even one party from one of these groups is lost, it could make the balance fall apart entirely. After Crocodile was arrested and got his Warlord title revoked following the Arabasta incident, the loss of such a powerful ally in such a public manner tips the balance away from the Seven Warlords of the Sea, and in turn, the Marines as well. This leaves them with diminished force to counter the menace of the Four Emperors and allows the general populace to question their power and authority.
Another concern is that the Marines are the sole organization completely under the supremacy of the World Government. The Seven Warlords often only follow orders on a whim, if at all, and the Four Emperors are outside of the World Government's control entirely.
The Four Emperors and Marines seem to be on the opposite ends of the spectrum, with the Marines being more orderly compared to the Four Emperors who are very chaotic, with the Seven Warlords acting as somewhere in between. Considering that these organizations are stated to be a balance and the fact that the loss of Crocodile threatened the balance, it is likely these groups are approximately equal in strength. According to Yosaku, the presence of the Three Great Powers over the Grand Line is what makes it the "Pirates Graveyard".
As the delicate balance of the Three Great Powers is what stabilizes the world, the existence and actions of other powerful groups, such as the Revolutionary Army and the Worst Generation is a significant threat to that balance. With the current dissolution of the Seven Warlords system, it is currently unknown how much the balance of power has been affected within the world. While several civilians express such concern, the World Government had utilized the Special Science Group (特殊科学班 Tokushu Kagaku-han?), or SSG for short, as a means to replace the Seven Warlords, expressing confidence it will restore the delicate balance. However, with two of the Emperors, Kaidou and Linlin, allying together for world domination, they express their confidence in toppling the entire World Government and the Three Great Powers' balance.
After the death of Gol D. Roger, powerful pirates began consolidating power in the New World. These included Roger's rival, Whitebeard, his old apprentice, Shanks, as well as Big Mom and Kaidou. Together, they became known as the Four Emperors, whose incredible force proved to be a major threat to Marine Headquarters.
In order to combat the growing threat of the Four Emperors, the World Government established the Seven Warlords of the Sea, seven strong pirates granted special privileges by the government, as a means of balancing power between the emperors and Marine Headquarters. Members included Shanks' rival, Dracule Mihawk, as well as Jinbe, Crocodile, Donquixote Doflamingo, Bartholomew Kuma, Gecko Moria, and Boa Hancock. This, in turn, gave birth to the "Three Great Powers".
At some point, they also attempted to recruit Portgas D. Ace as a warlord, but he refused. Ace then visits Shanks to thank him for saving Luffy's life and informs him that he plans on taking Whitebeard's head. He fought with Jinbe before encountering Whitebeard himself, who then recruited the young pirate into his crew.
Sea of Survival: Super Rookies Saga
East Blue Saga
Dracule Mihawk travels to the East Blue while chasing after Don Krieg, thus encountering both Luffy and Zoro for the first time. Later on, Luffy defeats Arlong, who was previously released from Impel Down by Jinbe's request. Afterwards, news of Luffy's accomplishments reach Marine Headquarters, and they issue him his very first bounty. Mihawk then pays Shanks a visit to inform him of Luffy's infamy.
Upon entering the Grand Line, the Straw Hat Pirates end up at war with the criminal syndicate known as Baroque Works, which was secretly led by Crocodile himself. They eventually arrive at Arabasta to help Princess Vivi stop Crocodile from destroying her country. They also meet up with Ace, who was still searching for Blackbeard. After being defeated by Luffy and having his crimes exposed, Crocodile was stripped of his status as a Warlord and arrested, causing a major fracture within the Three Great Powers.
Sky Island Saga
After Crocodile's expulsion from the Seven Warlords, a meeting is arranged between the Fleet Admiral of the Marines, Sengoku and several Vice Admirals, along with three Warlords, Doflamingo, Kuma and Mihawk, to discuss the situation. Laffitte managed to sneak into the meeting to propose his captain, Blackbeard as a replacement for Crocodile. Meanwhile, Shanks attempts to contact another of the Four Emperors, Whitebeard.
Water 7 Saga
On Long Ring Long Land, the Straw Hat Pirates encounter Admiral Aokiji, who easily defeats Luffy, but chooses to spare him out of gratitude for stopping Crocodile. Then, at Enies Lobby, CP9 leader, Spandam accidentally issues a Buster Call, prompting Vice Admirals Strawberry, Yamakaji, Doberman, Onigumo and Momonga to appear and bombard the island, though the Straw Hat Pirates manage to escape. Later on at Water 7, they are then visited by Luffy's grandfather, Vice Admiral Garp, who unsuccessfully attempts to arrest them.
Despite the efforts made to prevent it by the World Government, Shanks was able to meet with Whitebeard to request that Ace stop his search for Blackbeard, only to be refused. Meanwhile, Ace finally finds Blackbeard on Banaro Island and duels with him, with Blackbeard being victorious. He then turns Ace over to the World Government, thus becoming Crocodile's replacement as a Warlord.
Thriller Bark Saga
The Straw Hat Pirates then end up at Thriller Bark, where they fight and defeat Gecko Moria and his army of zombies. But then they were swiftly defeated by Bartholomew Kuma, who leaves them all alive.
Summit War Saga
After assaulting the World Noble Saint Charlos, Marine Headquarters sends in Admiral Kizaru to apprehend them, but they were then rescued by Kuma by sending them away to far away locations. Luffy was sent to Amazon Lily, where he encountered Boa Hancock and unintentionally made her fall in love with him. She then assists him with getting to Impel Down so that he could save his brother, Ace from being executed. There, he ends up releasing both Crocodile, who was interested in killing Whitebeard, and Jinbe, who had been imprisoned for opposing Ace's execution. Using his status, Blackbeard also infiltrates the prison and recruits prisoners Catarina Devon, Vasco Shot, Avalo Pizarro and Sanjuan Wolf, as well as former Head Jailer, Shiryu.
The arrest of Portgas D. Ace, the second division commander of the Whitebeard Pirates, resulted in the Marines entering into hostilities with the Whitebeard Pirates. This eventually led to a major battle between the Marines and Seven Warlords against the Whitebeard Pirates and their allies. This was the first known instance where any of the powers went into full-out conflict with one another. Prior to the battle, Kaidou tried to attack Whitebeard and was intercepted by Shanks, causing a dispute between the Emperors.
During the war, Jinbe officially resigns from the Seven Warlords. Despite the great effort to rescue him, Ace was killed at the hands of Admiral Akainu. Whitebeard himself would also meet his end at the hands of Blackbeard, who also resigns his position as a Warlord and uses an unknown method to steal Whitebeard's power from his corpse. After Whitebeard's death, the balance collapsed and the world entered into chaos, contrary to the belief that the great pirate's death would ensure peace.
At the conclusion of the Summit War of Marineford, the Five Elders deemed Gecko Moria as "too weak" to retain his status and ordered Donquixote Doflamingo to eliminate him, though Moria escapes. Furthermore, both Monkey D. Garp and Sengoku resigned after the Summit War of Marineford.
During the Timeskip
During the timeskip, all three groups underwent changes. Admirals Akainu and Aokiji dueled for the right to become Sengoku's successor. Sakazuki won and has been promoted to Fleet Admiral, while Kuzan resigned from his position as Admiral. Trafalgar Law, Buggy, and Edward Weevil were appointed to fill the three vacant positions of the Seven Warlords of the Sea.
In order to cope with the loss of Whitebeard's protection, Jinbe contacts Big Mom, who agrees to make Fish-Man Island as part of her territory in exchange for a monthly supply of sweets. He and his crew also agree to become her subordinates.
A year after Whitebeard's death, his old crew, led by Marco and Blackbeard Pirates clashed in the Payback War. The Blackbeard Pirates ultimately emerged victorious, and the Whitebeard Pirates have not been seen since. This event, combined with the Blackbeard Pirates conquering the majority of Whitebeard's former territories, leading to the World Government acknowledging Blackbeard as Whitebeard's replacement in the Four Emperors.
Eustass Kid and his crew fought with the Red Hair Pirates and he ended up losing an arm. He, as well as Urouge, then attacked the Big Mom Pirates and injured one of their Sweet Commanders, but were then forced to flee. Capone Bege joined under the Big Mom Pirates and married one of Big Mom's daughters while both X Drake and Scratchmen Apoo join under the Beasts Pirates.
The Final Sea: The New World Saga
Fish-Man Island Saga
After saving Fish-Man Island from being destroyed, two members of the Big Mom Pirates, Pekoms and Tamago arrive to collect their tribute of sweets, only to find that the factory was destroyed and all of the sweets have been eaten by Luffy, thus risking the island's destruction. Luffy then contacts Big Mom and grants her all the treasure they collected in exchange for the island's safety. Big Mom reluctantly agrees to this deal and decides to vent her rage out on Luffy instead. Luffy then declares that he will beat Big Mom and make Fish-Man Island his own territory.
At Punk Hazard, the Straw Hat Pirates meet with Trafalgar Law, who decides to form an alliance between the crews to take down Kaidou. Working together, they defeat Caesar Clown, who was aligned with Doflamingo to produce SMILEs for Kaidou's army, as well as Vice Admiral Vergo, who was secretly one of Doflamingo's subordinates.
At Dressrosa, Law's status as a Warlord was revoked due to forming an alliance with the Straw Hat Pirates. Doflamingo would also lose his status as well after being defeated by Luffy and having his crimes exposed.
Four Emperors Saga
Monkey D. Luffy infiltrated Whole Cake Island in order to retrieve his chef, where he allied himself with the Fire Tank Pirates, in an attempt to assassinate Big Mom, which ended in failure. However, both crews managed to escape her territory, with Luffy's actions indirectly destroying her base. He has since been known as the "Fifth Emperor".
During the Levely, Kings Nefertari Cobra and Riku Doldo III brought up the facts that their respective countries suffered because of the Seven Warlords of the Sea, which led to the heated debate and ultimate passing of the notion of dissolving the Seven Warlords organization. As part of the action, large fleets of Marines were sent to arrest Buggy, Dracule Mihawk, Edward Weevil, and Boa Hancock.
The end of the Seven Warlords system led to a majority of the world cheering, with civilians believing that allying with pirates was a grave mistake to begin with, and many pirates being fed up with the arrogance of the group. A few, however, became worried at the resulting imbalance of the Three Great Powers. The Marines hope the SSG will successfully replace the Seven Warlords as part of the Three Great Powers.
Big Mom entered Kaidou's territory, Wano Country, in pursuit of Luffy. When the two Emperors came face-to-face, they started fighting each other, with the World Government hoping they would inhibit themselves. However, much to their shock, the two ended up allying with each other. It was then revealed during the Fire Festival, that they were launching New Onigashima Project, where they would enslave the remaining populace of Wano, turning the island into a pirate paradise, before aiming for the Ancient Weapons and the One Piece and ultimately initiating the "Final War". However, just after Kaidou killed his longtime ally, Kurozumi Orochi and obtaining the former shogun's forces, the Beasts Pirates headquarters of Onigashima came under attack by the Ninja-Pirate-Mink-Samurai Alliance.
- One Piece Manga and Anime — Vol. 45 Chapter 432 (p. 7) and Episode 314, Garp explains the Three Great Powers.
- One Piece Manga and Anime — Vol. 8 Chapter 69 and Episode 31.
- One Piece Manga and Anime — Vol. 95 Chapter 957 (p. 3) and Episode 958.
- One Piece Manga and Anime — Vol. 66 Chapter 650 and Episode 570.
- One Piece Manga and Anime — Vol. 67 Chapter 659 and Episode 583.
- One Piece Manga and Anime — Vol. 70 Chapter 700 and Episode 629.
- One Piece Manga and Anime — Vol. 80 Chapter 802 and Episode 751.
- One Piece Manga and Anime — Vol. 82 Chapter 821 and Episode 773.
- One Piece Manga and Anime — Vol. 72 Chapter 713 and Episode 643.
- One Piece Manga and Anime — Vol. 79 Chapter 792 and Episode 735.
- One Piece Manga and Anime — Vol. 80 Chapter 801 and Episode 746.
- One Piece Manga and Anime — Vol. 95 Chapter 956 (p. 13-17) and Episode 957, The Seven Warlords of the Sea are officially disbanded.