Alien Vendetta started out as a solo project from Norwegian Doomer and speedrunner Anders Johnsen. The original plan was for something closer in scope to Hell Revealed but it slowly drew away as Anders began to invite other authors to the project, among them his close friends, eventually landing in between something more like what are now considered the "classic" Doom II megaWADs of '96-'97 and more obvious slaughter combat a la Hell Revealed. Like any Doom PWAD, it doesn't need a story, but there's one included in the intermission texts. I'm not entirely sure, but it looks like the UAC has been working with Hell. The demons pull a double-cross, of course, eliminating their benefactors, taking over UAC installations, and then mounting an offensive which you naturally must repel and then push back to where it came from.
