Nazjatar Empire

The Nazjatar Empire is the naga civilization beneath the Great Sea, formed by Queen Azshara and her followers in the wake of the Great Sundering and the birth of the naga race.

The naga of Nazjatar are masters of sorcery and natural dwellers of the ocean deeps.

=Birth of the Naga=

Following the events of the Great Sundering, when the remaining Highborne were transformed into naga, they built a new city under the waves of the Great Sea. Under the direction of their ever-pragmatic Queen Azshara and Lady Vashj, they set about constructing a new capital where Zin-Azshari and the Well of Eternity were once located. Thus, Nazjatar was created, and Azshara knew that one day her empire under the sea would eclipse even that of the ancient night elves.

Return of the Legion
Queen Azshara sent a force led by Tidemistress Athissa to Azsuna on the Broken Isles to retrieve the Tidestone of Golganneth. Azshara herself appeared before Prince Farondis when Farondis tried to save an adventurer captured by the naga and tried to convince him to kneel before her, but Farondis fought Azshara off. The naga at the Eye of Azshara summoned a creature known as the Wrath of Azshara after retrieving the Tidestone of Golganneth, but ultimately lost and the Tidestone was retrieved by the adventurer.

=Battle for Azeroth=

The naga attacked the shores of Kul Tiras and Zandalar. Later, Queen Azshara opened the waters of Nazjatar trapping the Alliance and Horde in the naga domain.

See WoWPedia