In order to face the horrible attack on the Federation outpost, a group of strong warriors on two starships, have been assigned to go there, stop that attack, and bring the troopers and leaders safe back to earth, but once everything changes when a starships Alesia, has been mysteriously disappeared.
If you're going to make an animated sequel to a live-action film, why not do something really terrific? You could create a world that would be difficult to reproduce in a live-action film. Instead, "Starship Troopers: Invasion" is just a boring quickie.