There's many campaigns which are all the objectives on each "world." For example: on Geonosis, there's the campaigns to eliminate Sun Fac, infiltrate the droid factory, destroy the droid factory, advance to the Core Ship, and infiltrate the Core Ship. Each campaign is made up of many mini-levels or, as I'd call them, checkpoints.
But there's only three "worlds": Geonosis, the RAS Prosecutor (not really a world since you're on a ghost ship), and Kashyyyk. Geonosis and the RAS Prosecutor are not tied into RotS at all. The first Kashyyyk mission is the demo mission, so once you get there, if you don't want to see any RotS-sensitive content, stop there.