Warning: Contains spoilers for One Piece chapter #1052
Rather than saving Wano Country by taking down the tyrant Kaido, Luffy and his Straw Hat Pirates might have sealed the fate of the island forever, in the latest of the great plot twists that made Eiichiro Oda's One Piece so successful. The Marines and the World Government have put Wano in their sights, which means that Wano could be erased from the maps, and Luffy won't be there to defend it.
The Wano Arc's conclusion was everything that One Piece fans hoped for. After a long and hard-fought battle, Luffy and the Ninja-Pirate-Mink-Samurai alliance took down Kaido and his Beasts Pirates, freeing Wano and restoring its rightful Shogun, Kozuki Momonosuke. The country had been controlled for twenty years by Kaido, who allied with the usurper Orochi and turned Wano into a giant weapons factory and the base for his army, making the inhabitants labor as slaves and suffer from disease and starvation. Kaido chose Wano as his stronghold to take advantage of the fact that the country had been following a strict policy of isolationism for centuries, which made it unaffiliated with the World Government. However, Kaido's defeat has finally attracted the attention of the World Government and its military branch: the Marines.
Chapter #1052 of One Piece shows that one of the powerful Marine Admirals, Ryokugyu, is headed toward Wano. One of the prerogatives of an Admiral is that he can order a Buster Call, a military attack performed by a fleet of Marine ships who open fire on a target (usually an island) until nothing and no one is left standing. In the past, two islands have been leveled by a Buster Call, Ohara and Enies Lobby, and both times it was to protect the World Government's secrets by eliminating Ohara's archeologists and its last survivor, Nico Robin. Robin is on Wano at the moment, and she is still a primary target for the World Government. Also, the country is hiding some important secrets from the past of One Piece's world (as teased by Oden's journal). Finally, the World Government wants to eliminate Luffy after he awakened his Devil Fruit, something that the Five Elders dreaded happening.
Regardless of the reason, Wano is at risk of being destroyed. This is a consequence of Kaido's downfall because the Yonko was so powerful and feared that the country was indirectly protected by his presence. This is very similar to what happened to Fish-Man Island, which was under Big Mom's protection until the Straw Hats arrived and put an end to that, exposing the country to potential dangers. Luffy and his friends are always portrayed as liberators, but they never stick around to see the consequences of their actions. Wano could be the first case in the series where the Straw Hat's interference turns into a tragedy rather than a triumph. Suffering under Kaido's yolk was terrible, but annihilation is an even worse fate.
Wano's fate depends on a series of factors. Luckily, Momonosuke's decision to not open the country's borders means that the Marines are still unable to take it over by force. However, Ryokugyu could have hostile intentions. If the Straw Hats are still on Wano when he arrives, then there is a chance that readers will be treated to an epic battle between them and a Marine Admiral whose powers and strength are yet unrevealed. The crew, however, is in rough condition, so they could not be able to stop the Admiral. In any case, the World Government is the most powerful organization in the One Piece world: if they decide that Wano is an enemy, then Luffy will not be remembered as the country's hero, but as its destroyer.
Look for One Piece's newest chapter when it releases on Viz Media's Shonen Jump app!