Xebel has had two different origins. Originally it was an other-dimensional kingdom ruled by Mera but it's history has been changed and is now a penal colony of Atlantis, where King Ryus rules.
Originally Xebel was an other-dimensional underwater kingdom ruled by Mera which got taken over by her nemesis Queen V'lana.
The penal colony of Xebel is part of the kingdom of Atlantis, which lies within the Bermuda Triangle and is reportedly inescapable by those trapped within the dimension.
Recently Siren, Mera's sister, has escaped with several Xebel soldiers, with an intention to kill Aquaman. She reveals Mera had originally been sent to kill Arthur, but failed in her job. It is also revealed they did experiments on a boy named Jackson Hyde, who is the son of Black Manta, Aquaman's arch-rival, and Jackson's mother. This meant that Black Manta killing Aquaman's and Mera's son; Aquababy was not just because of Mera, like Mera had blamed Arthur. His mother died in the experiments but Jackson survived and gained powers from it. He has joined Aquaman as Aqualad. Siren and the Xebel soldiers have taken their fight to the surface, attacking a sunny beach full of people, claiming that everything on land belonged to them because life started in the oceans. Aquaman and Aqualad try to fight the large amount of soldiers attacking and save the "land-dwellers" from the Xebel soldiers.