A demesne was the playing board of the game Shah-tezh. Emperor Sheev Palpatine used this concept to explain the Galactic Empire to a young Gallius Rax twenty five years prior to the Battle of Jakku.
By the design of the game, all pieces exist to protect the Imperator, and if the Imperator falls a game must begin anew. By analogy, if the Emperor were to meet his demise, the Empire would be dismantled and begin anew via the Contingency, since those serving the Empire failed their utmost role of protecting their leader. Following this design, Counselor Gallius Rax, a title perhaps eponymous of the Shah-tezh piece, exhorted Grand Admiral Rae Sloane to travel to the Eclipse, a Super Star Destroyer forging a path through the Unknown Regions.