Ruling over the seas while maintaining a delicate balance between order and chaos, the Three Great Powers in One Piece are the Marines and the World Government, the Seven Warlords of the Sea, and finally, the Four Emperors. Each of the individual factions constituting this trio have their own agendas and objectives, but they have been known to ally with one another when their purposes align. First alluded to by Yosaku, one of Zoro's friends during his days as a bounty hunter, the Three Great Powers are the strongest military powers in One Piece, stabilizing the seas and preventing any disruption to the world order. Among the three, there is a well-defined progression from the authoritative banner of the World Government, to the controlled disorder of the Seven Warlords, and then, the lawless freedom enjoyed by the Four Emperors, who answer to absolutely no one. While their relative strengths are yet to be completely illuminated, they are comparable in most respects, especially when considering the unsteady alliance that once existed between the World Government and the Seven Warlords.
After the death of the Pirate King Gol D. Roger, a number of his former adversaries — such as Big Mom, Kaido, and Whitebeard who were once part of the Rocks Pirates — journeyed to the New World and established dominion over territories, laying the groundwork for what would become the Four Emperors. Eventually, Roger's apprentice Shanks also traveled to the second half of the Grand Line and made a name for himself, to round out the quartet of the most powerful pirates in the world. The growing threat posed by these individuals alarmed the World Government, who might not have been able to face up to them, even with the combined power of the Marines and the Admirals at their side. Hence, this prompted them to set up the Seven Warlords system, which enlisted powerful pirates in their service, in return for special privileges as well as their own territories in the Grand Line. This was the scenario at the beginning of One Piece, however, the status quo has undergone great changes with the intervention of Luffy and his crew. With this in mind, let's delve into each of these groups to explore how their role in maintaining this stalemate over the seas has evolved over the course of the story.
The Marines
Enforcing the World Government's authority over the seas, the Marines are the foremost military force in the world. They are responsible for maintaining order, enforcing the laws of the World Government, and hunting down pirates and other criminals. Led by the Fleet Admiral, who is the highest-ranking officer in the organization, the Marines have powerhouse combatants such as the three Admirals, who are the strongest and most skilled officers in the hierarchy, and the Vice Admirals, who serve as high-ranking commanders and advisors. Some Marines are in possession of Devil Fruits, as in the case of Akainu, Fujitora, and Ryokugyu, whereas others such as Garp and Koby rely exclusively on their mastery of Haki. The Marines have a significant presence throughout the world, with bases and strongholds located in many different countries and territories, powerful weapons and ships, and a vast network of intelligence agents and informants. Their most prominent stronghold is the Marine Headquarters in New Marineford in the New World, where the most high-ranking officers in the Navy are stationed.
In their efforts to maintain order and hunt down pirates, the Marines often clash with the Straw Hat Pirates and other groups of pirates who challenge their authority. There is also internal conflict within the ranks of the Marines, owing to the uncompromising ideals of the World Government, the corruption within the organization, and their role in protecting the World Nobles. While some Marines such as Akainu have an uncompromising and extremist view on enforcing justice, others such as Garp, Smoker, or Fujitora see things in a more balanced light, and are not completely averse to defying the government's corruption in service of the people they are sworn to protect. It is speculated that the Navy is on a somewhat equal footing with the Four Emperors, which prompted the government to take matters into their own hands and enlist external agents to back up their authority.
The Seven Warlords Of The Sea
Also referred to as the Shichibukai, the Seven Warlords of the Sea are a group of elite pirates who have been recognized for their strength and granted special status by the World Government. The warlords serve as privateers for the World Government and maintain order in their respective territories by hunting down and conducting offensive operations against other pirates as per the order of the World Government. Given a range of privileges and benefits, including immunity from prosecution by the World Government, the warlords have access to resources and funds, and the ability to call on the Marines for assistance if necessary. In exchange for these benefits, they are expected to follow the orders of the World Government and to work towards its interests. However, their relationship with the government is not as well-defined as may seem at first glance, and many among their number do not always heed the call of the Navy, or even act in defiance of their superiors from time to time.
Over the course of the series, several members of the Shichibukai have resigned or been removed from their positions after losing to the Straw Hats and other pirate groups, including Crocodile, Gekko Moriah, and Donquixote Doflamingo. Others such as Jinbei, Trafalgar Law, Buggy, or Blackbeard, gave up their posts of their own volition, as they had goals which were in direct opposition to the World Government. For instance, Jinbei's desire to elevate the standing of Fishmen saw him return to Fishman Island and eventually join the Straw Hats as a helmsman, Law and the Heart Pirates set off on their own to find the One Piece, and Blackbeard became a Yonko after stealing Whitebeard's Devil Fruit and territories. On the other hand, the former warlords Buggy, Crocodile, and Dracule Mihawk banded together to form Cross Guild, a pirate organization devoted to hunting down Marines by issuing bounties on their heads. Furthermore, at present, the Shichibukai system has also been abolished after the events of the Dressrosa arc, leading to a massive shift in the power dynamic of the One Piece world. In the aftermath of this move, the World Government is now attempting to replace the Seven Warlords with the Seraphim project spearheaded by Dr. Vegapunk and his Special Science Group (SSG), which has created controllable clones of the former members of this group.
The Four Emperors
Compose of the four most influential and infamous pirate captains in the One Piece world. Also known as the Yonko, the Four Emperors are neither allies nor enemies, and exist in a state of fragile balance, each one trying to gain an advantage over the others while also fending off the attacks of the Marines and other pirate crews. The original quartet of Pirates consisted of Shanks, Whitebeard, Big Mom, and Kaido, but the events of Marineford and Wano, particularly the defeat of Big Mom and Kaido, created a new lineup that now includes Luffy, Blackbeard, and Buggy, with Shanks being the only member to retain his place. The Emperors are not interested in taking over the world or ruling over it in any way, but they are also not afraid to challenge the authority of the World Government when threatened, or in the pursuit of certain objectives.
They also have a complex relationship with the government, where certain Emperors such as Shanks are open to using diplomacy as a means to deal with the Marines, others such as Luffy, Kaido, and Blackbeard rely exclusively on force to get their point across. This makes them unpredictable and dangerous, and it is one of the reasons why the World Government considers them to be such a threat. As the story continues to unfold, it will be interesting to see how the Four Emperors continue to shape the world of One Piece and how their actions will impact the future of the series.