Despite the controversy, the Alderaan security forces managed to keep order until the crown prince was assassinated; just days later, the Queendied heirless. The Parliament of Alderaan was deadlocked on which of the noble houses should inherit the throne. Civil war erupted when House Thul, backed by the Sith Empire, decided to settle the matter by force.
The civil war ceased to be internal when a forgotten house returned with Imperial backing and the Republic started funneling support to the House Organa. Even though neither superpower officially had any troops on the ground, Alderaan became a site of conflict between them in the post-war galaxy.
Bouris Ulgo protested House Thul's return, stating that they're just puppets for an Imperial invasion, and attempted to rally the other houses to expelling Thul once more. But as the houses were too fractured to realize it, Ulgo decided to take action by usurping the throne from the Panteers. This only caused all the houses (excluding House Rist) to turn against him as well.
There were ongoing peace talks between the Houses at a secret location, but the Jedi envoy, Sidonie Garen of House Organa was infected with a madness plague, and she nearly escalated the war further until Yuon Par's Padawan, the futureBarsen'thor, as envoy to Teral stopped her. The Barsenthor then negotiated the summit to agree to a truce and to reconvene at a later date. The Hero of Tython also helped to preserve talks between houses Thul and Organa by saving the life of the Head of House Thul from the Death Mark Superweapon, utilized by Lord Nefarid to escalate the conflict.
Eventually, Bouris Ulgo was captured by an elite strike team. It was later discovered that Houses Ulgo and Rist were behind Gaul Panteer's death.
Alderaan Civil War is also the name of a Warzone in the game Star Wars: The Old Republic. Set on Alderaan during the civil war period, Republic and Imperial teams fight to control heavy laser cannons in a strategic battlezone, hoping to use those cannons to destroy the opposing faction's troop transport.