Based on the last chapter, here is my speculation:
So we know he aimed to be the king of the world. Probably he kidnaped the 5 kings in order to negotiate with the gorosei. Maybe not right away asking to take the world but asking to have a country of his own (just like bb) as his first stepping stone. All of that just to accidentaly find out that there is someone ruling behind the shadow as the real king of the world. He didnt do anything maybe becasu he knows that he wouldnt win against Imu.
Just a speculation tho