Demarco Colony was a Colony located within Zeon Space at Nexus Sector, that was mainly known as the largest Colony of the Principality of Zeon within the Nexus Sector. The Colony was in close proximity to both Sierra Colony and Side-9, and was known to be an official Metropolitan Colony that contained the most cities and less farmlands. However despite having less Farmlands, Demarco still held plenty of Countryside areas including forests lakes and rivers on a wide scale.
The Colony was Invaded by the Zenora Empire, in the early months of the Zeon Civil War, and became an official battleground between the Principality of Zeon and Zenora forces. However after about 9 days of heavy fighting the Principality of Zeon after receiving new training and ways on how to take on modernized mobile suits, had been successful in pushing the Zenora out from Demarco from both within and outside the Colony.
Their victory is short lived when the Zenora Empire turned Gryps II toward the Nexus Sector and fires the Colony Lazer against Demarco shooting a hole straight through the outside of the Colony and causing the entire interior to collapse from within on January 1st, UC 0097, killing all inhabitants and Zeon forces that were no longer in Mobile Suits.
The Destruction of Demarco mixed with the Side-9 Massacre, scarred the Principality of Zeon, with Heirshy even recounting the memories of Operation British, on how the Principality had conducted the same thing against the Federation during the early weeks of the One Year War, when they conducted a Colony Drop on Sydney Australia, that wiped out 16 percent of the continent.
Demarco's destruction would forever haunt Heirshy and most of the Principality of Zeon Aces who took part in the Engagement, further prompting more hatred and attacks against the Zenora Empire in the future.
Demarco's shattered broken remains, had become a memorial site in UC 125 about 3 years after the Zeon Civil War had ended, and had since then been remained Barren.