The Twentieth Army, also known as Emerald Banner Command, was a Republic Sector Army in the Grand Army of the Republic during the Clone Wars. Headquartered at Tallaan, the 20th was one of the Southern Campaign Sector Armies, and was charged with the defense of Sector 20, later known as the Tapani Oversector, which contained the beginning of the major hyperlane called the Rimma Trade Route.
During the Clone Wars, the 20th Sector Army fought a back-and-forth war with Separatist forces along the Rimma and the Corellian Trade Spine, especially near the Separatist strongholds of Thyferra and Bestine. Near the end of the war, the 20th gained the upper hand when General Grievous pulled many of the area's assets out of the region to use in his raid on Coruscant.
When Supreme Chancellor Palpatine declared himself Emperor, Emerald Banner Command became part of the Imperial Military. By 2 BBY, Emerald Banner Command was under the control of the newly-appointed Grand Admiral Octavian Grant.