[Editor's note: Some mild spoilers are discussed for The 100 Season 7 in the below interview.]

On the series finale of The CW series The 100, entitled “The Last War,” Clarke (Eliza Taylor) and her friends have reached the final battle, a culmination of all of the fighting, bloodshed and loss that they’ve experienced. But if they can’t find a way to overcome all of the impending violence, then humanity might be doomed forever.

During this 1-on-1 phone interview with Collider, show creator Jason Rothenberg (who wrote and directed the final episode) talked about the likely tears and cheers that viewers will experience, the spectacle and scope of the ending, when he knew how things would wrap up, whether Bellamy’s (Bob Morley) story might have played out differently in other circumstances, the show’s complex mythology, how he came to make his directorial debut with the last episode of the series, and what he personally learned from the experience of running The 100.

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Photo by Colin Bentley/The CW

Collider: What can you say to tease what fans can expect from the finale? What should they be bracing for? What emotions do you hope they have?

JASON ROTHENBERG: Well, there definitely will be tears. Hopefully, there will be some cheers. I’m hoping that people will be surprised by certain things, maybe some people that they haven’t seen in awhile. They should expect some spectacle and scope as our finales are want to do and this is no exception. And I feel like they should expect some closure to the story, as well, and not be left feeling like too much is untold.

When did you know what the endpoint of the series finale would be? At what point did the full picture come into view?

ROTHENBERG: Things come into real clear focus as you are breaking a season, but then things change and decisions are made. I began to know what I wanted the show to feel like at the end, near the end of Season 5. The feeling at the end of Season 5, of some kind of hopefulness, was definitely what I was aiming for here too, in a different way, of course, but just tonally. It began to take shape then, and then we convinced the network and studio to let us end the show, as opposed to getting canceled or continuing forever. We wanted to know that we were ending, so that we could play to something specific. That’s when it really began to take shape and everything started to become clearer.

How did you let the cast know where their stories would be ending, if they made it to the series finale? Did you just give them that final script or did you have conversations with them before that?

ROTHENBERG: Every season, I always had a conversation at the beginning of the season with the cast about how the season was going to go. This season was no exception. The difference was that this season there were some big changes. I don’t think anybody was surprised when they read the final script. At that point, everybody knew what was happening with their character. Still, seeing it is different than me telling you about it. But if you look at the season document that we write every season, most of the end points for those characters didn’t change, despite the fact that there were quite a few big internal changes throughout the season.

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Photo by Bettina Strauss/The CW

How much did the lesser amount of time that you had with Bob Morley affect the journey and outcome for his character? Would you have done things differently with him, if you had him for every episode, or do you feel like his story still would have always concluded in the way that it did?

ROTHENBERG: It’s hard to say how it would have concluded. It definitely would have been very, very different. We had a whole season mapped out, and then had to change it at the last second. When you’re making a television show, you have to roll with the changes and you have to roll with circumstances that are not in your control and try to do the best job you can because you can’t stop the presses. The show must go on. So, it would have been very, very different. Maybe at some point in the future, I can talk about how it would have been different but I don’t think that’s useful.

How hard was it to make that decision to have Clarke kill Bellamy to save Madi only to have something so tragic happen to Madi?

ROTHENBERG: How hard? It wasn’t hard. On some level, it obviously is heartbreaking and heightens the futility of violence and death, which the show is always trying to do. We were always trying to tell the story as emotionally as we possibly could. And so, hard is not the word I would. We just never pulled any punches creatively on this show, for better or worse.

In this last season, we got a sense of how complex the mythology of this show is. Was it always in the plan to have the mythology be so complex or was that a result of you building on each season, the longer you got to explore the story?

ROTHENBERG: Definitely B. Building up the mythology is a really good way to put it. We tried to plant seeds for what was coming in the next season, in each season. As we would sit down to build out the world of that season, the details and arc would get filled in. That was really the process. We did not have seven books that were laying out that mythology from. That was something that we did ourselves, as the story unfolded.

You had never directed and then ended up taking on the last episode of the series. What went into that decision and what was that experience like?

ROTHENBERG: Especially following making a prequel pilot during the season, it was crazy. It was definitely the hardest season for me, in terms of the work level and workload. For so many reasons, it was the hardest season of all of them. But I also knew that if I didn’t do it, I would have regretted it. I’m really, really happy that I got to it and that I got that experience. What I learned certainly coalesced in directing that episode, leaning on the people who know their jobs better than I do and letting the actors do their thing. My DP this season, Gerald Packer, was so amazing and it was about literally letting him do his job. Up and down the cast and crew, everybody brought their game and made it easier for me and made me look good. I jokingly said, “I’m basically taking my first at bat in the world series.”

What do you feel like you’ve personally learned from telling this story for seven seasons, and being the showrunner for this show and this cast and crew for all of these years? What has that been like for you, personally?

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Photo by Bettina Strauss/The CW

ROTHENBERG: My God, it’s been the education of my life and my career, for sure. I went into this having one episode of television produced as a pilot, prior to The 100 pilot, and I entered day one of the first season of the writers’ room as the creator/executive producer of a show but I had the same amount of experience as the staff writer who was there for a day. I had a huge, huge, huge learning curve through Season 1, and then I took over as showrunner in Season 2. One of the things I learned is that you have to lean on people. You have to lean on your more experienced colleagues. You have to trust that a director is going to elevate things sometimes when maybe the script isn’t quite there. You have to lean on the other writers to elevate when perhaps the break wasn’t exactly what it should have been. You have to lean on the actors to bring things to life and trust that they’re going to. You can’t do it all yourself. It’s impossible. So, you try to hire the best you can and television gods willing, it all works out. It sounds like a cliche but it’s true. I caught the wave of this show and I rode it all the way to the shore, and here we are.

The 100 airs on Wednesday nights on The CW.

Christina Radish is a Senior Reporter of Film, TV, and Theme Parks for Collider. You can follow her on Twitter @ChristinaRadish.