The Devastation of Manaan was an act carried out by the Sith Empire during the Great Galactic War against the planet Manaan, sometime between 3681 BBY and 3653 BBY. After centuries of hiding in sectors of space unexplored by the Galactic Republic, the Sith returned to the known galaxy and initiated their crusade against the Republic's member worlds and other planets. In their campaign for dominance, the Empire traveled to the water world of Manaan, a planet known for its staunch devotion to neutrality during periods of war. The Sith refused to accept the native Selkath's tradition of impartiality and bombarded the planet, destroying almost all of Manaan's free-floating surface structures. As a result, the Selkath species entered a period of extreme isolation from the galaxy, and it was many years before they reestablished contact with the rest of galactic civilization, though they remained wary of both the Republic and the Sith Empire.
Manaan, as seen from orbit
After several centuries of self-imposed exile in the far reaches of the Outer Rim Territories, the Sith revealed themselves and their rebuilt Empire to an unsuspecting galaxy in 3681 BBY, sparking the Great Galactic War. The conflict between the Sith and the Galactic Republic saw the Imperials achieve major victories while the Republic crumbled under political infighting and economic depression.
During the war, the Empire also came into conflict with fiercely independent societies, such as the Selkath of Manaan. Manaan was a water-covered planet with a long avowed neutrality during instances of galactic conflict—during the Jedi Civil War of the Old Sith Wars era, the native Selkath managed to maintain their impartiality and broker their kolto healing agent to both the Republic and Darth Malak's Sith Empire. The Empire, seeking to take sole the source of kolto, demanded Manaan's allegiance. The Selkath instead responded with an offer of neutrality similar to the one used during the Jedi Civil War, but the offer only angered the Empire.
In response to the Selkath's proposal of neutrality, the Empire bombarded Manaan from orbit, sinking almost every surface structure—including their capital of Ahto City. During the attack, Vinyor Tesh's mother and father, who were both researchers based on the planet, were killed. A Jedi named Laotah was visiting the planet at the time and took the young orphan to Coruscant to be trained as a Jedi at the Jedi Temple. The Republic was unable to lend aid on account of their being at war, and feeling betrayed, the Selkath retreated back into the seas of Manaan in a mass exodus, leaving their floating cities abandoned and in ruins.
The Sith attack, which historians later labeled as "the Devastation of Manaan," and lack of Republic aid gave rise to feelings of hostility towards off-worlders among the Selkath, who came to consider all foreigners—regardless of whether they were of the Empire or Republic—as slavers and enemies. The Selkath spent many years in isolation from the galaxy, and the Force-using Order of Shasa came to power as Selkath's protectors. In their isolation, Selkath culture thrived, but some began to seek the economic benefits that came from trade with off-worlders. The Mon Calamari diplomat Mahreen spent several years convincing a delegation of the Order of Shasa to meet with her; the Selkath also found their economy to be declining and began discussing the issue amongst themselves.
When they finally decided to end their isolation, Mahreen convinced the Selkath to convert one of the few remaining surface structures into the Mercantile Plaza, a trading plaza with strict rules as to who was granted landing privileges. At first only ambassadors from the Republic were permitted, but the Selkath politician Shuuru eventually extended an invitation to the Sith Empire, as he distrusted the Republic due to their inactivity in Manaan's time of need. Ahto City remained in ruins for decades, and the Selkath established the Manaan Special Warfare Group as a fledgling defense force for their planet, though the intelligence forces of the Sith Empire considered the organization to be insufficient to repel an invasion. Around 3626 BBY, the Sith Empire began marshalling their forces to invade the planet in their ongoing renewed war with the Republic; the Empire's Dark Council considered the act to be retribution for the planet's refusal to adequately share their kolto reserves.
The devastation of Manaan was first mentioned on the official website for the LucasArts video game, Star Wars: The Old Republic. The information could be found on "The Setting," a webpage intended to provide background on the game's historical period. Since its establishment in 2008, The Old Republics website has gone through a number of changes, resulting in the removal of some of the text that was originally located there. "The Setting" was updated mid-2011, and the information on Manaan was removed. It was later expanded on in promotional material for Game Update 2.9 of The Old Republic, which introduced a Flashpoint based on Manaan, and in entries of the in-game Codex discussing Manaan. An in-universe intelligence report, posted on the game's official website on July 30, 2021 as part of the setup for the forthcoming Legacy of the Sith expansion, canonized the event's name.