Zack Snyder revealed why Army of the Dead's mercenary group needs money in a world seemingly overrun by zombies.

During a live Q&A following the release of the Army of Dead trailer on Netflix, Snyder was asked about the film's central conceit involving a vault heist in Las Vegas in a world with the living dead. But as the director and co-writer of the movie explained, it's not the whole world that's full of the undead, it's just Vegas.

"The basic premise is that the zombie outbreak started in Vegas. And the way that the outbreak was contained was a wall of shipping containers was built around it, and that they kept the plague inside, that was how they contained it with this big wall," Snyder said of the film's plot. "And so, hence the zombie birds. And so you have this, that's the world that we have to enter... it's been like that for a few years. And so when Vegas fell, it was on fire, got bombed, there was like a bit of a war in Vegas. That was a big part of the mythology of the world. And so into that world, when we enter that world, we have to get gunned up. And there's a whole set of rules around the world."

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Snyder elaborated on creating a universe with its own set of rules, saying, "I really wanted to make a movie that, with the universe... I kind of can be the extreme authority on, and therefore, allow the audience just to be on a ride. And that is purely by design."

For the director and writer, the opportunity to create a universe for audiences to get invested in was a big deal. And Netflix certainly seems interested in expanding that world. The streamer has already ordered a prequel film and anime series based on Army of the Dead to fully flesh out Snyder's zombie concept.

The official synopsis for Netflix's Army of the Dead reads:

Following a zombie outbreak in Las Vegas, a group of mercenaries takes the ultimate gamble, venturing into the quarantine zone to pull off the greatest heist ever attempted.

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Directed and co-written by Zack Snyder, Army of the Dead stars Dave Bautista, Garret Dillahunt, Ella Purnell, Omari Hardwick, Raul Castillo, Tig Notaro, Theo Rossi and Ana de la Reguera. The film will release on Netflix May 21.

Source: Netflix