Complex sentence: The Kuun-Lan comes under attack from pirates who also want the siege cannon, during the battle, the Caal-Shto (which has been subverted by The Beast) arrives and destroys or takes over the pirate force.
Split into simpler sentences: The Kuun-Lan comes under attack from pirates who also want the siege cannon. During the battle, the Caal-Shto (which has been subverted by The Beast) arrives and destroys or takes over the pirate force.