Earlier on in the movie development stage of the third Captain America film, before it became Civil War, there was talk of giving it a zombie-type story. Captain America almost took on a horde or zombies! How awesome will that be! That might have happened if Robert Downey Jr. didn’t sign on to reprise his role as Tony Stark, a.k.a. Iron Man. As you know his contract with Marvel was up when Civil War came around, so they had to renegotiate a deal with him, and if things had gone south on that, Captain America and Iron Man would have never faced off.
During an interview with EW, directors Joe and Anthony Russo, Joe explained:
“It was not a given that we were even going to do Civil War when we were talking about the next movie after Winter Soldier. So there was a period of time when we explored possibilities for Cap stories that did not include it. We spent a few weeks doing that, although Civil War came up fairly early in the process and once that happened it took over our brains and we ran hard at it.”
He went on to explain how an early version of the story would have included zombies, and it was inspired by a 1976 comic 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. It didn’t have anything to do with Civil War, 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. … The charm of the Madbomb is that you turn hordes of people into berserkers. That was the physical challenge that Cap and company would have had to face.
“The notion of the Madbomb would have been Cap having to fight civilians and how he would he handle that. 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?”
“Somebody you know has turned into a zombie and now you have to fight them, and there would have been the emotional component of that.”
The report offers some insight into the Madbomb and what it entailed, saying:
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.