The attack from the Star Destroyer drove these Demon Kings into a fury, rendering them somewhat irrational. They even considered joining forces to bombard and sink a continent. Anyway, that continent had already been occupied by Earth's Evolvers, and keeping it was of no use.
However, the Demon Kings who retained their sanity knew that if they recklessly unleashed the Demon King's Power within the Demon God Realm, they would destroy themselves before the Earth's Evolvers came, and then the enemy wouldn't need to do anything but wait at the cross-border point to capture them all.
"Can't even counterattack, are we Demon Kings just going to sit and wait for death? In a pinch, we could abandon the Demon God Realm, charge into Earth, wipe out those despicable Evolvers, and turn Earth into a second Demon God Realm." A Demon King couldn't stand this indignation and proposed a fairly decent plan.
"The premise is that we win this battle before we talk about occupying Earth."
