One of the most prominent moments in One Piece so far was the death of Whitebeard during the Marineford arc. His death signalled the start of a new pirate era, and was capped off with an even more intriguing power from Blackbeard. Ever since Blackbeard mysteriously stole Whitebeard's Devil Fruit power, and revealed he could dual wield two different powers, he's been a strong point of interest.
What was even more surprising was seeing just how much Blackbeard advanced his status in the pirate world during the time skip, and now he stands as one of the Four Emperors of the Sea. The latest episode of the series helped to clear up how he got there by showing what Blackbeard did after killing Whitebeard.
In Episode 890 of the series, Marco the Phoenix makes a return to the anime and it's revealed that he's been keeping an eye on Whitebeard's hometown. It turns out that Whitebeard had been keeping an eye on it throughout his entire pirate career, and Marco has taken up the mantle as its protector now that he's passed. Speaking with Nekomamushi, Marco reveals that Blackbeard went on a tirade after killing Whitebeard.
He started attacking all of Whitebeard's now free to claim territory and kicked off the "grudge war" with the remaining Whitebeard Pirates. But he was too powerful to take down, and subsequently used both of his Devil Fruit abilities to claim all of Whitebeard's territory. Though this isn't a complete picture of how he rose to power, it's clear that Whitebeard's Devil Fruit abilities made Blackbeard stronger than ever before.
So with two powerful abilities and the stolen Whitebeard territory, it's easy to infer that Blackbeard continued this tirade through the two year time-skip. It's why he was able to easily slip into the open position as one of the four Yonko. It might be awhile before fans get to see Blackbeard again, but it's clear he's going to be a dangerous future foe for Luffy and the Straw Hats.
Eiichiro Oda's One Piece first began serialization in Shueisha's Weekly Shonen Jump in 1997. It has since been collected into over 80 volumes, and has been a critical and commercial success worldwide with many of the volumes breaking printing records in Japan. The manga has even set a Guinness World Record for the most copies published for the same comic book by a single author, and is the best-selling manga series worldwide with over 430 million copies sold. The series still ranked number one in manga sales in 2018, which surprised fans of major new entries.