Zombies are the new Nazis, at least when it comes to video games. The handoff couldn’t have been more straightforward. In World at War, the 2008 iteration of the wildly popular Call of Duty series, the game designers, perhaps sensing that players were tiring of the pleasures of killing the soldiers of the Third Reich, introduced a new mode: Nazi zombies. Shooting already dead members of Hitler’s army proved even more satisfying than doing the same to (digitally) living but historical Germans. Out with World War II, in with World War Z.

The lineage isn’t quite that simple, of course. Zombies have a long history in games, including seminal titles like Resident Evil (1996) and Wolfenstein 3D (1992), widely regarded as the original first-person shooter, which itself was about fighting some kind of undead/Nazi hybrid. And apocalyptic fiction has become unavoidable in post-Sept. 11 America, no matter the medium. The zombie subgenre is nearly as popular in novels and films as it is in video games.

What’s distinct about the video game strain of the infection is that “zombies” and “Nazis” are usually interchangeable concepts. Each is presented as a dehumanized enemy that won’t make players feel guilty for all the exultant violence they inflict. The zombie apocalypse neatly removes thorny questions of morality and makes the action about as fraught as gobbling the ghosts in Pac-Man or blasting the descending aliens in Space Invaders.

Even a game like last fall’s Tea Party Zombies Must Die, in which the (presumably liberal) player is asked to lay waste joyfully to the likes of Bill O’Reilly and Sean Hannity, depends on this understanding. By turning conservative personalities into zombies, and thus making it not only acceptable but also acceptably exciting to shoot them, “the game scripts its violence into morally excusable self-defense,” as Peter Freeman wrote recently in a thought-provoking essay on games in Crisis, the Roman Catholic journal.