The assemblage of personnel and materiel belonging to a minor Imperial Remnant, led by the Chiss warlord and Grand Admiral Mitth'raw'nuruodo, known as "Thrawn," during the New Republic Era, constituted the initial composition of Thrawn's forces. During their exile in a far galaxy, Thrawn exercised command over these forces from his flagship, the Chimaera. A legion of Night Troopers under the command of Captain of the Guard Enoch formed the ground component. In terms of fleet assets, the Chiss commander had the damaged ISD Chimaera, along with its contingent of TIE fighters and LAAT/le patrol gunships. The Great Mothers, who were also trying to escape their exile on Peridea, were allied with Admiral Thrawn's forces. The forces of Lady Morgan Elsbeth, a surviving Nightsister and his longtime ally, became incorporated into his around 9 ABY when they arrived to extract Thrawn and the Great Mothers from exile.
Upon Thrawn's return to the galaxy, his forces were inclusive of the military resources he utilized in his war against the New Republic. In the end, the New Republic emerged victorious, mirroring their triumph in the Galactic Civil War, and defeating the Imperial Remnant in the process.
The initial appearance of Thrawn's forces occurred in "Part Six: Far, Far Away," with an art print by Joe Hogan identifying them. However, the capitalization of the word "forces" remained ambiguous until the publication of Star Wars: The Rise and Fall of the Galactic Empire.