Dominion section was an unofficial name for a small Confederate Marine Corps unit, part of the 33rd Ground Assault Division, led by Arcturus Mengsk. He chose the name because he thought it was "appropriately grand".
After a period of time on Pridewater, the unit's first combat action was at Turanga Canyon in August, 2480 (a period where its members were supposed to be on leave) where it was attached to a larger force of neurally resocialized marines under the command of Captain Angelina Emillian. It was to act as a "smart" counterweight to the resocialized troops. On its way to the canyon where the Confederates would attack a Kel-Morian Combine-operated deep core mining operation, the transport carrying them was shot down, severely injuring Emillian and putting nineteen-year-old Lieutenant Mengsk in charge. Mengsk won the battle, but not without wasting the lives of the resocialized troops.
Over the next several years the unit continued to steal Kel-Morian mining operations and act as heavily armed backup to local enforcers, serving on worlds such as Parragos and Pho-Rekh. In 2485, Dominion section was attached to an Alpha Squadron company led by Captain Edmund Duke during the Battle of Noranda Glacier, where Chun Leung and Toby Mercurio were both killed in action. Yancy Gray was killed later on Artesia Prime. The three remaining members survived the Guild Wars and headed their separate ways.
The section's namesake may have provided the inspiration for the name of Mengsk's future government, the Terran Dominion.