Maintain Balance of Power

The so-called "bottom line" was the foundation for both parties to maintain tacit cooperation. Now, Ferde and the Isle of Dawn's cooperation was built on the fact that both had to face the Destruction Army. In other words, the Isle of Dawn wouldn't mess around while the humans, led by Ferde, were facing the Destruction Army.

Once the Isle of Dawn felt that Ferde was a great threat, they might possibly break this tacit agreement.

Eliard didn't believe this. "Would they really?" he asked.

Vance shrugged. "I can't be certain, but from how they treated Evelina, they really care about their so-called tradition and noble bloodline. They might even see it as a glory they must protect with their life. They're probably able to do anything if their tradition is threatened."