Cocoon's people started stealing resources from Gran Pulse. Pulsians thought the technological advances Cocoon was making would lead them down a path of evil, and Cocoonians thought Gran Pulse was a primitive and hellish world full of savages. Eventually, a war erupted, and Cocoon won.

[she's trying to keep a smile up, but the pain in her eyes is noticeable. it's something very personal to her, after all.]