Russo brothers reveal Captain America: Civil War was almost a 'zombie' movie 

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had not been able to explore the clash between Team Iron Man and Team Cap – and it would have involved Chris Evans’ hero facing down a demented zombie-like horde.

Directors Joe and Anthony Russo tell EW that during Marvel Studios’ development of the film, there was fear that one half of the

conflict might not be in the movie. Robert Downey Jr.’s contract with the company had been fulfilled, and a new deal was being negotiated to keep him in the fold – but both sides were playing hardball.

“It was not a given that we were even going to do

when we were talking about the next movie after

. So there was a period of time when we explored possibilities for Cap stories that did not include it,” Joe Russo says. “We spent a few weeks doing that, although

came up fairly early in the process and once that happened it took over our brains and we ran hard at it.”

They made this alternate-history revelation during a conversation about the in-home release of

, which is available as a digital download on Sept. 2 and as a Blu-ray collection on Sept. 13.

So, from the start, everyone’s first choice was to do a version of the now-classic 2006-2007

comic book series penned by Mark Millar, which had hero facing off against hero in a battle over who controlled the superpowered. But without Downey and Iron Man, it would have lacked the emotional heft and tension that had been built up between Steve Rogers and Tony Stark over the course of the previous films.

Another story would be necessary in that case, and Marvel’s braintrust turned to another classic Cap story from January 1976 that was written and illustrated by Jack Kirby…

“There was a period where we did discuss a third act that revolved around the Madbomb from Cap mythology,” Anthony Russo said. “It didn’t have anything to do with

, and if we couldn’t get Downey – in the very, very early conversations before we nailed him – somebody pitched the idea of a third-act that revolved around the Madbomb, which makes people crazy. It almost like zombifies them – but not literally.”

In the comics, it was an A-bomb-like device that came in different sizes and used sonic waves instead of radiation blasts to cause its devastation. It didn’t demolish buildings – it wrecked the minds of everyone in proximity, turning them into a mindless zombie mass, although its victims were still alive and just violently out of their minds rather than undead.

“The charm of the Madbomb is that you turn hordes of people into berserkers,” Anthony said. “That was the physical challenge that Cap and company would have had to face.”

In Kirby’s story, the Madbombs were devised by a wealthy secret society known as the Elite, who planned to set off a massive one during the American bicentennial, reducing the country to anarchy so it could be rebuilt as an oligarchy. (Rich guys dismantling democracy by stoking unhinged rage in everyday Americans until they turn on each other? How far-fetched!)

The fascist footsoldiers of the Elite’s Royalist Forces of America helped enact the plan and were prepared to enforce order on the devastated country after the dust and madness had dissipated.

If the film version had happened, the Russos say villain Baron Zemo (ultimately played in

by Daniel Bruhl) would have been the one setting off the Madbomb. Cap would have had to destroy it and reverse its effects to save the same frenzied mass of people that were attacking him.

“The notion of the Madbomb would have been Cap having to fight civilians and how he would he handle that,” Joe Russo says. “We were always trying to put him into these interesting moral conundrums because of his nature. That would have made a compelling third act because if civilians are the antagonists, how could he stop them without killing them?”

, this storyline would also have pitted hero against hero, since some of Cap’s friends would have also fallen victim to the Madbomb’s powers.

“Somebody you know has turned into a zombie and now you have to fight them,” Anthony says. “And there would have been the emotional component of that.”

Then… Downey and Marvel Studios reached a deal.

“So we threw the Madbomb concept off the table,” Joe says. (It did come back as part of the climax to Season One of ABC’s

Downey’s deal also includes his participation in a third and fourth Avengers film,

and its follow-up, which the brothers are currently prepping to shoot in Atlanta. Cameras start rolling in December and

The still-untitled sequel will come out May 3, 2019, but both will shoot back-to-back.

“We’re shooting them simultaneously because they share a lot of similar cast and the time constraints and trying to get that scale of cast together is extremely difficult,” Joe says. “It makes the most sense to shoot them simultaneously.”

The brothers emphasize, however, they are two different stories – not one tale split in two.

“Time will make clear the connection between the films and how they’re different,” Joe says. “That’s all we’re going to say. People will discover it as the years unfold.”

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