Though powerful in their own right, much of the Yonko's martial strength can be attributed to their elite and abundant crews, as well as to their close alliances with other pirate captains. Whitebeard's crew amounted to over 1600 men and he also had 43 subordinate New World pirate crews to aid him in his efforts to rescue Ace, each headed by an infamous pirate captain. Some of these subordinate captains were very powerful in their own right, as seen with Little Oars Jr.'s impact as a key player for the Whitebeard Pirates during the Battle of Marineford.
Due to the sheer size of their crews, most of the Yonko utilize several elite commanders to lead their forces; Whitebeard originally had sixteen division commanders (each leading 100 men), Kaido has his three Disasters, Big Mom has her Three Sweet Commanders, and Blackbeard, who originally only had a small crew of under ten men prior to his becoming a Yonko and expanding his crew size drastically, later has it subdivided through his Ten Titanic Captains, some of whom were members of his original crew. As seen with top Whitebeard commanders' Marco, Ace, Jozu, and Vista's skirmishes with the Shichibukai and Marine Admirals during the Battle of Marineford, these top officers are seen to be able to contend with the elites of the other two Great Powers. Due to their exposure and feats as executive officers for the Yonko, the commanders are regarded as a huge threat by the Marines, second only to their Yonko captains. Thus far, the three highest known active bounties all belong to Yonko commanders (Cracker and Smoothie of the Big Mom Pirates at Beli860,000,000 and Beli932,000,000 respectively, and Jack of the Beasts Pirates at Beli1,000,000,000) while interestingly, none of the Yonko themselves have had their bounties revealed.
Because of their power, the Yonko can declare chosen locations as their own; the mere declaration is often enough to compel others, both Marines and pirates alike, to acknowledge and respect the Yonko's authority; when Whitebeard declared the crime-ridden Fishman Island to be under his control, he immediately ended all pirate attacks on the island as well as its slave trade.
Accordingly, they each have a large territory that they govern within the New World. The Yonko provide protection to all who reside within their territories, keeping the borders safe from any faction that may wish to invade them. Big Mom's territory, Totto Land, is heavily protected by scouting ships and by watchtowers called Tartes that dot the coastlines of each of her islands, both prepared to inspect and potentially shoot down any ships not affiliated with her crew. She also has territorial sea slugs that patrol the waters, warning would-be intruders that they are entering her territory. Finally, Big Mom has 34 ministers as part of her administration, one to run the affairs of each of her territory's subsidiary islands.
It is only with the combined efforts of the Marines and the Shichibukai, as well as the distrust amongst them, that keeps their power in check. During the Battle of Marineford, the Marines and Shichibukai needed to fight together just to engage one of the Yonko, Whitebeard, his crew, and their allies. The arrival of a second Yonko, Shanks, immediately brought an end to hostilities, showing the power and influence they have without even needing to engage in combat.
The Yonko themselves are not allied together as a coalition compared to the Shichibukai, and follow their separate agendas. Nevertheless, most of the Yonko still seem to have the intention of becoming the Pirate King and finding One Piece, with former Yonko Whitebeard being an exception. The possibility of two or more of the Yonko forming an alliance was enough of a threat to cause the World Government to panic, seen when it unsuccessfully attempted to prevent a meeting between Shanks and Whitebeard. The World Government feared that the two Yonko would unify, creating a much more imposing threat that would disrupt the balance between the Great Powers.
They can motivate others to partake in a life of piracy; Shanks personally inspired Luffy, and the death of Whitebeard inspired many pirates to travel to the Grand Line.
After the timeskip Trafalgar Law cited that there are only two methods of surviving in the New World, and that is to be protected under the umbrella of a Yonko's dominion and become their ally or to constantly oppose their authority. At least Teach and Kaido are both gaining influence and strength in the form of amassing Devil Fruit powers, both in their own unorthodox methods. Big Mom intends to increase her crew's power by forming an alliance with the legendary Germa 66 and gain access to their advanced technology.
Because of their immense power, it is necessary for factions aiming to oppose them to first strike an alliance with other factions in order to bring the Yonko down. However, even with multiple alliances amongst powerful pirates, the chances of defeating a Yonko are still extremely low; when the Straw Hat Pirates and the Heart Pirates formed an alliance to defeat Kaido, Law informed Luffy that he believed their chance of success was only 30%.
Yonko Charlotte Linlin and Kaido both have a single Road Poneglyph that can, with all four Road Poneglyphs deciphered, lead to Raftel's location.
Whitebeard was active on the seas during Gol D. Roger's voyage across the Grand Line; he was said to be one of the few people who could rival Roger, as well as the man closest to One Piece after Roger's death. However, he had no intention of finding the treasure.
Throughout his life, Kaido was defeated seven times by the Marines and other Yonko. However, all of their attempts to execute him were unsuccessful.
Some of the Shichibukai have fought the Yonko in the past; Shanks and Dracule Mihawk frequently dueled in their younger days, Gekko Moriah fought Kaido, and Crocodile fought Whitebeard.
Twelve years ago, Shanks visited Luffy's hometown. It is unknown if the title of Yonko existed at that point in time or if he was one at the time as well.
About four years ago, Kaido formed a partnership with Donquixote Doflamingo and Caesar Clown so that the two would give him Artificial Devil Fruits known as SMILEs, which he used to create an army of Devil Fruit users known as Gifters.
All of the Yonko seem to have strong fleets, including huge ships and elite crewmen. At some point, they all traveled to the New World where they are currently locked in a stalemate, unable to progress any further into the Grand Line. This is a product of the combined efforts of the Marines and the Shichibukai, as well as the presence of the other Yonko. A particular reason for their inability to reach Raftel is the fact that one needs all four Road Poneglyphs to determine its location; one is possessed by Kaido, one possessed by Big Mom, one is located on Zou, guarded by the Mink Tribe and the last one is in an unknown location.