Suggest me a book where the protagonists defeats evil, just to turn evil themselves.

“Whoever fights monsters should see to it that in the process he does not become a monster. And if you gaze long enough into an abyss, the abyss will gaze back into you.”

I'm looking for books where the protagonist/s overthrow the evil state, just to become as evil themselves. I prefer the grander plots, but it can also be on a personal scale. I prefer scifi or fantasy.

A good example of this isThe Blade Itself trilogy. Superman: Red Son, although a movie, is another good example.