NEW YORK — Brad Pitt wanted to build a better blockbuster.

During the years Hollywood shifted toward increasingly bigger spectacles and superhero tentpoles, one of the movies' biggest stars largely stayed on the sidelines, focusing instead on ambitious ensembles ("The Tree of Life," "Inglourious Basterds") and unlikely dramas ("Moneyball").

But the zombie apocalypse "World War Z," which opens Friday, is Pitt's bold, long-gestating, big-budget effort to enter the franchise fray. It's his attempt to engineer not just a disaster thrill ride like 1974's "The Towering Inferno" (a beloved film to Pitt, who saw it repeatedly as a kid growing up in Missouri), but to make a thought-provoking action flick filled with geopolitical questions.

It's been a humbling crusade.

"These films are much more difficult than I realized," Pitt said in a recent interview over coffee at a restaurant off Times Square.

Based on the 2006 sci-fi novel "World War Z: An Oral History of the Zombie War" by Max Brooks (son of Mel), the $200 million-plus film has had a rocky path to theaters. It's gone through a swarm of screenwriters, several key crew changes, a postponed release date and, most notably, a reshot ending.

But most moviegoers that make it to the film — far from the flop many predicted — will likely wonder what all the fuss was about. As Pitt's producing partner Dede Gardner points out, no one ever says: "Honey, let's go to this movie this Friday. I swear it was on-budget and on-schedule."

The reviews have largely been positive for "World War Z," a riveting, brisk thriller with a refreshingly — and, for summer movies, atypically — human protagonist who relies purely on his intellect and experience as he shuttles around the world trying to solve the zombie pandemic that's engulfed most of the planet. Pitt's former United Nations investigator has no superpowers, no gun, and as Pitt says, "can't even run that fast."

It may sound paradoxical, but though "World War Z" is awash with gruesome hordes of snarling zombies, it is — alongside Superman and Godzilla-sized sea monsters — one of the most human-scaled blockbusters of the summer.

While Hollywood awaits the film's box office performance with bated breath, Pitt is confident. He's shaped the film as a producer since his production company, Plan B, acquired the book rights in 2006.

"I know it works," the 49-year-old actor says. "I know everyone involved is going to be happy. It's just a question of how happy. We're proud of it. When you get involved with a film like this at this scale, at this cost, there's more responsibility to meet that number immediately."

Not unlike his character, Pitt has been flying around the world to promote "World War Z." He spent Father's Day with his family, but at 40,000 feet, he says. "I've got a few countries to go," he says with a grin.

Though he acknowledges the film has been "a learning experience," he's upbeat, repeatedly citing the "good fun" of making a big movie for the multiplexes. Adapting the book — a series of first-person dispatches from around the globe — required not just finding a narrative drive to the story, but capturing the novel's theorizing of how self-interested nations would fare in a global catastrophe. (Faring well, for example, is walled-off Israel, the location of the film's most extreme set piece, shot in Malta with some 900 extras.)

But in the end, the principles of making a popcorn-friendly movie often bested the filmmakers' higher ambitions. Much of the allegory had to be cut.

"It got too dense," Pitt says. "We got too weighed down on it. We spent a couple years on it. We couldn't get it into one movie. We had to walk a line between using the film as a Trojan horse for some of that, but these things have to be fun. And we were bored, ourselves."

Instead, the filmmakers, including director Marc Forster ("Quantum of Solace," "Stranger Than Fiction"), wrestled with finding what Pitt calls "the pace of the summer action film, the cadence it needs."

"Movies have a DNA," says Gardner. "They have their own identity. This one just fought back. It fought back, ultimately, in a way that I really appreciate because it sort of met our ambitions for it with its own ambitions."

The most painful part of taming "World War Z" was deciding that the third act — a large-scale battle with the zombies in Moscow's Red Square, filmed in Budapest — didn't work. It was a gut-wrenching realization, made after the filmmakers and Paramount executives screened the film.

"It was abysmal," says Pitt. "It was really painful. What it means is that after you've put in that much work, you go, 'Oh, we're so far away.' It just means we got a lot more to go. You go home, you have one too many beers and you get up the next day and you go, 'OK. This is what we got to do.'"

While tinkering with a movie in post-production is normal, hiring screenwriters (Damon Lindelof, Drew Goddard) to write an entirely new ending is quite uncommon. Instead, a more quietly tense sequence set in Wales was constructed, with production resuming for a $20 million reshoot.

"We just decided it wasn't good enough," says Gardner. "I see that as a good thing. We were very fortunate to have partners at Paramount who were interested in doubling down. I can't tell you how grateful I am for that."

The need for such a reshoot, though, contributed heavily to early perceptions of the film. While Pitt admits the production was initially difficult, he says once solutions were found, the process was "really fun." (Forster was not made available for this article.) Gardner, too, chafes at what she calls the unfair over-scrutinizing of the film.

"You often hear of the artists in a studio not getting along," says Pitt. "This was absolutely a really nice experience. (Paramount) has been so supportive and came to the table with great creative ideas."

Whether "World War Z" will spawn sequels, as was the initial hope, will have to wait for the box-office response. In a packed summer schedule, the film will have to compete with "Man of Steel" in its second week of release.

After a long battle with "World War Z," Pitt (who'll this fall star in David Ayer's World War II thriller "Fury") says he's just "not really the franchise kind of guy."

"We spent so much time on this," he says. "We've got so many good story lines stemming from the book or inspired by the book and then just generated from our own powwows. It might still be fun. We've got enough material, that's for sure. We'll see, we'll see how this works, we'll see how everyone feels afterward."