The DLC is the fifth story expansion and is heavily story driven, with many personal phases and cutscenes, and less focus on farming and questing in open world environments.
Onslaught puts players in the middle of the reignited war between the Galactic Republic and the Sith Empire. Because of the crisis that ensued as a result of this, the alliance commander has the chance to decide the fate of the galaxy. The Sith Empire prepares to strike a new Republic shipyard on the new planet Corellia. The Republic forces must defend Corellia from the Sith with help from the entire galaxy.