Kevin Costner explains that jam-packed Horizon — Chapter 1 ending montage

Warning: This article contains spoilers about Horizon: An American Saga — Chapter 1.

The first part of Kevin Costner's magnum opus to the American West has arrived — and parts of it may have left you with some questions.

Horizon: An American Saga — Chapter 1 follows a diverse array of characters, including massacre survivor Frances Kittredge (Sienna Miller), calvary man Trent Gephart (Sam Worthington), rustler Hayes Ellison (Costner), wagon train leader Matthew Van Weyden (Luke Wilson), and Apache warrior Pionsenay (Owen Crow Shoe).

The conclusion of Chapter 1 brings many of those characters to the start of a fresh page in their journeys. Tensions rise on the wagon train after two men ogle Juliette Chesney (Ella Hunt) while she's bathing; Marigold (Abbey Lee) abandons Hayes to go off with a gambler she hopes will offer her protection after leaving Ellen Harvey's child with a Chinese family; the aggrieved settlers of Horizon attack a group of Apache and claim scalps for revenge; and Frances kisses Trent, finally pushing forward the simmering attraction between them.

But Costner didn't want their stories to feel totally unfinished either. "I didn't want to create a cliffhanger," he tells Entertainment Weekly. "They got a complete story, but it's really clear that it's going to go forward because the complete story is embedded there with it."

Partly, Costner is referring to the film's final montage, a dizzying array of images spliced between shots of a printing press rolling off more fliers for the town of "Horizon" as their maker, Pickering (Giovanni Ribisi), ponders the dream of the West he's selling to unsuspecting folks. Costner promises that a montage teasing the next chapter (he plans to make four total) will conclude each film.

As for Pickering, we'll see him pop up with increasing frequency as the story moves forward. "There are salesmen in every century, every decade," Costner adds. "People are being sent out there with a false sense of hope, and people are making money off people's dreams. He's one of a thousand that did that. But he will end up dominating Chapters 3 and 4."

And while the montage is a taste of what's to come, it's also a reminder of the central truth of the film — people will continue moving West no matter the cost. "I wanted to let people know that regardless of this terrible massacre, people are going to just keep coming, and the story is going to keep coming, and it's going to expand," says Costner. "And the reality is it's going to get harder. But the stories blossom. We fill out these people and do a pretty deep dive on who they are."

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With that will come new characters, but Costner also promises those who stick with the journey from the start will be more than satisfied. "I close all these loopholes," he says. "I go down these rabbit holes, and then I find a way to circle back so that if you're watching, you're rewarded with a level of behavior that tracks and plays into somebody's personality. I like to tie up loose ends, and this journey should be able to do that, but there are some people that come and go, and you lose them along the way."

That includes some actors being replaced by older actors when characters age, as Horizon moves to the end of the Civil War, which will come at the conclusion of Chapter 2.

Costner has previously said that the story of Horizon takes place over 12 years, but he wants to clarify that the movie doesn't move backward and forwards in that timeline unless via a clear flashback.

"I'm not trying to jump around too much," he says. "There's a flashback situation that occurs in each chapter, but the rest of it is linear."

Sharp-eyed audiences may have already noticed some hints of what's to come. For instance, Sienna's Frances shares a surname with a family journeying West on the wagon train. "There is absolutely a connection there," Costner teases. "And that becomes clear in the beginning of Chapter 2."

Chapter 1 is now in theaters, and Chapter 2 arrives on Aug. 16.