The anti-demon war in the northern Star Domain of Alliance, from the Oath Star campaign to its end, didn't last a long time, only six months.
From the perspective of time, this war was considered an outstanding victory.
The invading Chaos Demon Army was terrifying in scale, not weaker than the peak strength of the Iron Armor Battle Group during the Iron Armor War. It included some Chaos Starfield Warriors, powerful Chaos Possessed Demons, Slaughter Army... Its leader was a Demon Prince of Khorne, whose original form might have been an Interstellar Warrior from a Khorne Warband.
This single entity alone caused enormous damage to the human defense line.
The falling of three planets was related to him. Those worlds could still be held under fierce attack, but due to the direct assault by this Demon Prince, wielding two blood axes, enormous holes were knocked into the human defense line, leading to the total collapse of the planetary defense line.
