We knew it would happen again.

Yes, the alien attack.

Also the movie about the alien attack.

When “Independence Day: Resurgence” lands in theaters on Friday, June 24, carrying wanton, worldwide destruction in its wake, it will be reviving a long-dormant franchise that was never really a franchise: “Independence Day” — the 1996 blockbuster that rained terror and spectacular explosions on New York, Washington, D.C., and Los Angeles — never had a sequel, despite a sequel always seeming like the obvious move. Now, with its cities falling on cities, a giant unmoored Buddha crashing through Big Ben and an alien spaceship occupying most of the Atlantic Ocean, “Independence Day” is officially a franchise. Thanks to technology.

“I always thought of the original as a stand-alone film,” said Roland Emmerich, the prolific producer and director of such disaster/sci-fi features as “Stargate,” “The Day After Tomorrow” and “White House Down.” He said that the advances in computer-generated imagery were so “radical” it made a second movie all but irresistible. “It was as if, finally, technology had reached the level of my brain,” he said, laughing. “We weren’t limited. Slowly but surely the idea for a second ‘Independence Day’ grew.”

There have been a lot of changes over 20 years, especially among the movie’s characters, most notably former President Thomas Whitmore, the Gulf War vet who took a hands-on approach to defeating the murderous aliens of the first film.

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“It turns out that everybody who had this telepathic virus put in their brain for contact with the aliens has not ever gotten free of it,” said Bill Pullman, who again plays Whitmore. “For him, as the years have gone on, it’s become more and more manifest, to the point that he’s a liability. The country is really trying to at least present this vision of world order and Whitmore had been a hero. But they can’t really put him out in public because he’s become paranoid.”

It sounds like a meatier role than one might expect from apocalyptic sci-fi. “It was really great,” Pullman said. “I couldn’t believe it. I said, ‘I have the best role in this whole thing!’ ”

His “Independence Day” co-star Jeff Goldblum also returns, as David Levinson, who was instrumental in defeating the aliens the first time around. He’s always known they were coming back.

“I was the MIT-graduated, underachieving cable technician, not interested in career glory, an environmental activist who got pressed into duty under extraordinary circumstances,” said the loquacious Goldblum of his character. “This time around they promoted me to director of Earth Security Defense and I’ve taken some of that downed technology we found, married it with our own, solved some of our climate change problems, helped rebuild a massively damaged planet — 3 billion were lost, if you remember, the first time around — and the family of man is at peace.”

Goldblum said he re-bonded with his co-stars from the first film, including Pullman, “my dad” Judd Hirsch and Brent Spiner, and got to know the new people like Sela Ward, who plays America’s first female president. “Liam Hemsworth, I got a big kick out of him, he’s a sweet, talented guy. And Charlotte Gainsbourg — wowwie wowwie, I spent some time with her. She’s terrific.”

Pullman said that in the initial drafts of the script, he and Goldblum had no scenes together. “Someone said, ‘There ought to be a scene between Bill and Jeff,’ ” he said. “So we got one, but the first versions of it were kind of perfunctory, with a lot of dump-trucking exposition and I was thinking, ‘Oh God, I wish they’d never said this.’ But then they kept getting better and then it became an important scene for both our stories, and in the end I think it felt worthwhile.”

The key cast member missing in action is Will Smith, for whom the original “Independence Day” was a career-making movie. (His character has been killed off.) Money, reportedly, was a factor in Smith’s absence, but Emmerich said there were other considerations.

“We’re going back like four years ago, and I totally understood why he said no,” Emmerich said. “He was shooting ‘After Earth,’ which was a father-son story, and our story had a father-son angle, so he felt he would be repeating himself too much.”

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There was also a point at which the movie wasn’t continuing at all, the director said, “but two years ago, two young writers” — Nicolas Wright and James A. Woods — “came along and unlocked for me the whole thing with a very simple trick: ‘You hand it off to the younger generation.’ And I said, ‘That totally works.’ ”

Emmerich admitted “I don’t like sequels” and “Independence Day: Resurgence” is his first. But it won’t be his last: “Independence Day 3” has already been announced.

“From the very beginning, the deal at the studio was that it’s very risky to do a sequel this late, after 20 years,” Emmerich said, “and I said, ‘If it works, we should do a second one.’

“They liked that idea,” he said. “And you can feel it in the film. That another story’s coming.”