Why doesn't the emperor want Gulliver alive anymore and how does this reveal the emperor's true nature?

At first, the emperor wants to destroy all of the enemy ships and therefore subject the people to be governed by a viceroy. Gulliver rejects the idea and tells him that he will never help place the people in slavery. The counsel agrees with Gulliver. The governor, who now seems to care for nothing but his own power, then decides that he doesn't want Gulliver alive anymore, since Gulliver won't help to kill the enemy.