LogFAQs > #966757146

It's a trope in a lot of "us vs. them" stories that "us" turn out to be the real villains in the conflict. It's a pretty easy twist to set up, since all you have to do is only show the viewer what the protagonist sees and limit the protagonist's perception to only see Us' point of view at the beginning of the story. Then the protagonist meets some Them in a non-combat setting, understands why Them is fighting and the lies Us told about how righteous Us' cause was, then conveniently the protagonist is also some kind of super-soldier who is able to single-handedly turn the tide in a dramatic final battle that secures a peaceful future for both Us and Them while deposing Us' corrupt leadership.

It's a very straightforward twist that's still effective because everybody loves a good betrayal and unmasking oppressive conspiracies, so it gets used a lot. Lies and betrayal are a very effective ways to build animosity toward a villain without being too heavy-handed in the exposition, especially if the victim is somebody the viewer is invested in.