Win or lose, the Dragon Slaying Empire will collapse. They can't survive without an enemy, and without an outside enemy, only themselves exist to attack.
Are there any other nations that are like this? The most popularly known one would be the Mongols, which turned into Russia. Could be fair to say the Roman Empire fits the bill too, but they were farmers at the core, so not an exact fit. Rome did need "tribute" from expanding though.