—Zephiel on War Dragons, during chapter 22 of The Binding Blade.
A War Dragon (戦闘竜, Sentōryū lit. Combat Dragon) are a type of mass-produced, artificial dragons which, as its name suggests, were bred specifically for war during The Scouring.
During the war, the dragons had one main weakness, that the humans heavily outnumbered them. Because of this, the Dragons near the end of the Scouring asked the neutral Divine Dragons for one of their own to turn into a Demon Dragon that would able to spawn the war dragons. The Divine Dragons refused, claiming that would be defying the laws of nature, and fled into the Nabata Desert, but one of them, a young female named Idunn, stayed behind and was captured. The Dragons then destroyed Idunn's soul so that she would follow their commands, and they began making War Dragons, which turned the tide of the war, until the Eight Heroes created their legendary weapons to pierce the dragon's scales. Eventually, the humans were able to defeat the war dragons and seal away Idunn.
1,000 years later Zephiel freed Idunn to conquer the world and then turn it over to the dragons, because he thought that humans and their emotions would lead only to the world's ruination, and that the War Dragons, without emotions, would be able to create a better world.
After freeing her, Zephiel entrusted Jahn, one of the last dragon survivors of the Scouring to guard Idunn and guide the new War Dragons. With Idunn following Zephiel's orders, she began making more War Dragons, which continued until Roy defeated Idunn and sealed away all of her memories as the Demon Dragon.
War Dragons are said to lack emotions altogether and to have little will of their own. It is said they know nothing but battle due to their purpose as soldiers for the Scouring. Ain, the only War Dragon to have dialogue, was shown to be capable of following simple orders and making battle tactics, but was confused by small talk.
War Dragons are noted to be weaker then true dragons, especially experienced soldiers such as Jahn. Instead War Dragons rely mostly on their ability to be produced in large quantities in a short amount of time.
- War Dragons appear very similar to Morphs in the prequel, though any explicit connection between them is unknown. However, Athos mentions that information on the creation of Morphs is of draconic origin.