The Great War was a series of conflicts that stretched from 3220 to 3224 that involved the Overland and the Kingdom of Acorn. Unofficially, other small nations joined in on the conflict, and some even joined the Overlanders in the hopes of filling part of the power vacuum. Technologically advanced, the Overlanders won victory after victory while the Kingdom was stuck with technology generally used by the Lost Million. Without need to fight wars, the Kingdom had not advanced much in the way of military might and were unprepared for the advanced mechanized units that the Overlanders had such as hover tanks, plasma cannons, and powered armor. At the most, the Kingdom could outfit their men with flak jackets and vehicles recreated from 22nd Century technology. As such, the war from 3220 to 3223 did not go much in the favor of the Kingdom.

The primary weapon of the Kingdom was the ancient M-18 rifle created after the Interplanetary War in 2163. These weapons were used by security teams of the Terra Nova expedition from Earth when disaster struck and the colony fleet ended up on what would be called Mobius eventually. The plans for this weapon were reused consistently over the years and while appearing ancient, focused fire could take down units with enough shots. Originally made by Colt Firearms, the newer models were crafted by the Kingdom with new stamping.

However, the Kingdom was pushed back to the Old City, Knothole. Were it not for the defection of Julian Kintobor, many believe that the Kingdom would lose the war. The usage of the SWATAU unit, later known as the SWAT Bot, would destroy a major part of the Overlander army. When news of the near annihilation of the army, enemy offense collapsed. Minor battles would occur in the later weeks, but many agree the war ended at the ancient capital of Terra Nova.