Warning! Contains major spoilers for One Piece chapter #1040
The stability of the world of One Piece is based on three "Great Powers": the Marine Headquarters, the Shichibukai, the Four Emperors. These are the major military powers, whose balance is needed to maintain world peace. After receiving a strong blow during the events of the "War for the Summit", that order has now been shaken to the core, as one of the Four Emperors is finally defeated by the pirates of the Worst Generation.
The Four Emperors (Yonko) are the four strongest pirates in the world, whose rule extends over the second part of the Grand Line, known as the New World. They are considered the closest to obtaining the title of Pirate King, and their military strength and their agendas put them among the top enemies of the World Government. Big Mom is one of them, the matriarch of the large Linlin clan and the ruthless ruler of the Totto Land country that she wants to make into a utopia in which all races of the world can live together. She is also a monster with unbelievable strength and the dangerous powers of the Soru Soru no Mi Devil Fruit, but her rule as a Yonko finally came to an end, thanks to the pirate captains Trafalgar Law and Eustass Kid.
During the Wano Arc, an alliance was formed between the samurai of the country and the crews of three pirates of the Worst Generation, Luffy, Law, and Kid, with the goal of taking down Emperor Kaido and ending his tyrannical rule over Wano. When Big Mom unexpectedly formed an alliance with Kaido, the situation looked dire, as two of the strongest pirates in the world had joined forces. However, the rebel forces' assault on Onigashima island continued, and the three captains had the job of taking down the Emperors. While Luffy took on Kaido, and their battle is still going on, Law and Kid cooperated to face Big Mom. Chapter #1040 of the manga shows the outcome of that fierce battle, as Linlin is defeated thanks to the two young pirates "awakening" their Devil Fruits, gaining increased powers.
This was not just a matter of the "good guys" getting a power-up to defeat the villain, however. The Emperors have been ruling for decades, and they are the main obstacles stopping the new generation from reaching their goals. Motivation is an important aspect for One Piece's characters: every major pirate has a dream they want to achieve, sometimes rooted in a tragic backstory, as is Law's case. Rather than a classic shonen fight, this was the first major instance of the new generation overcoming the hurdles put in their way, and moving one step closer to their goals. The title of this chapter is "Falling on Deaf Ears", to reinforce the idea that Big Mom's arrogance and sense of superiority are destined to crumble in front of the unwavering spirit of the young pirates.
If readers can suppose that Luffy will also win his fight against Kaido (the opposite would be unlikely at this point), then the order and peace of the world are really about to get shaken. Of the "Three Powers", the Schichibukai were recently disbanded by the World Government, which plans to substitute the group with its army of cyborgs, the Pacifistas. The Emperors were already shaken after Whitebeard's death during the Summit's War, but Blackbeard taking his place seemed to maintain order, for the moment. With the fall of Kaido and Big Mom, this will no longer be the case. It is very likely that the consequences of these tumultuous changes will be the subject of One Piece's next arc that, according to the manga's creator Eiichiro Oda, will show "the greatest battle ever".