The World Government is the most corrupt organization in One Piece, and it has been fooling people for centuries. Ever since its establishment, the World Government has committed all kinds of atrocities to keep its secrets from leaking. This involves murdering influential One Piece characters, altering historical records, and destroying entire nations.
The World Government was created when twenty rulers allied together to destroy the Great Kingdom. They treated the Great Kingdom as a threat, which prompted them to take action. The twenty kingdoms were successful in their objective, after which they formed the World Government. Out of the twenty rulers, 19 of them placed their swords around the Empty Throne as a sign of their loyalty. It also signified that they were all equal and that none of them was above the others.
The Missing Sword
Nefertari Lily, the queen of Alabasta, did not put her sword around the throne. She did not even stay in Marijoa and opted to go back to Alabasta. Lily's decision was bizarre, especially given the amount of power that the Celestial Dragons have. But she probably had very good reasons to turn down the offer and leave Marijoa. In One Piece Chapter 1085, it was revealed that Lily's full name was Nefertari D. Lily. This made her a member of the mysterious D family, which has been called the natural enemies of the gods.
In One Piece, the Celestial Dragons are considered gods, so the members of the D family are their enemies. Imu also stated that the members of the D family opposed the World Government in the past. They also disclosed that Lily made a massive blunder, which caused the Poneglyphs to be released into the world. Normally, it would be chalked off as a mistake, but the fact that Lily was a D makes it seem like an elaborate plan. Furthermore, it makes sense why Lily didn't want to stay in Marijoa. Imu knew about Lily's intentions and probably ordered her assassination, which is why she never made it back to Alabasta.
The Successor
It is a fact that Lily did join the other nineteen rulers, but at some point, she changed her mind. It is possible that Lily met Joy Boy, who told her about the true intentions of Imu and what it meant to be a D. Lily was convinced and decided to release the Poneglyphs so that the rest of the world would have a chance at learning the truth.
Unfortunately, Lily was killed before she could make her way back. However, she did leave behind a letter that was kept hidden in Alabasta. When Nefertari Cobra read the letter, he understood what he had to do. Cobra could not relay this information, so he implored Sabo to tell Vivi and Luffy about their lineage before being murdered in cold blood by Imu and the Five Elders. While this event was taking place in the Empty Throne room, Vivi was being held captive by CP0. Kalifa told the princess that she would very likely end up becoming the pet of a Celestial Dragon. Vivi began to contemplate her future when Wapol broke one of the walls and saved her.
Vivi's Duty
After this reveal, it is quite obvious that Vivi is going to play an extremely important role in the story. The death of Nefertari Cobra means that Vivi will have to take command of Alabasta and lead the country toward a new dawn. Vivi has several qualities that make her a worthy successor to Cobra. She is a headstrong woman who is not afraid to throw herself in the face of danger. Her heroics in the Alabasta arc endeared her to the citizens of the country, and they will have her back no matter what happens.
Currently, Vivi is traveling with Morgans and Wapol. The ruler of the Black Drum Kingdom saw Cobra being killed by Imu and the Five Elders, and it's safe to assume that he told Vivi and Morgans about it. This is reason enough for the World Government to kill Vivi, but she has been on its radar for quite some time now. When Imu was first introduced in the series, they had Vivi's picture in their hands. This suggests that the princess was a target before she found out the truth about her father's death. Imu considers Vivi a threat, which is why they wanted to eliminate her. Fortunately, Wapol managed to free her before CP0 could hand her over to the Five Elders. Vivi's next step will depend on what happens on Egghead Island. If the Straw Hats get out safely, Vivi might regroup with them because they protect her from any kind of harm. Vivi is also considered an honorary Straw Hat and this is the best time to go back to the crew. This would also explain why Oda decided to keep Yamato in Wano, as he wanted Vivi to be the next Straw Hat.