AMNA NAWAZ: Tomorrow marks 13 years since the beginning of the Syrian civil war.

What began as a civil uprising against President Bashar al-Assad is a conflict that's now killed an estimated half-a-million people.

One group fighting the Assad regime is the Islamic State, or ISIS, who also targeted journalists.

Jim Foley was an American journalist covering the war when he was kidnapped by ISIS terrorists in 2012 and publicly beheaded two years later.

His murder shocked the world.

A decade later, his mother, Diane Foley, tells Jim's story and how she came to be a leading advocate for Americans held hostage abroad.

That's all in her new book, "American Mother."

And Diane Foley joins me now.

Welcome back to the "NewsHour."

DIANE FOLEY, Co-Author, "American Mother": Thank you.

AMNA NAWAZ: So you have joined us here on the "NewsHour" many times to talk about Jim, to talk about the extraordinary work that you do.

What was it that told you had to pull all of this together in a book right now?

DIANE FOLEY: I really think the way we remember where we have been and our challenges going forward is by telling stories.

Jim was a storyteller.

All that you do, you help us remember what is happening in the world.

And Jim, it was time.

I was feeling that it's been 10 years.

Some people were children when this happened to Jim.

And we have accomplished a lot as U.S. government.

I'm so grateful for all the good people who stepped up and made it happen, donated, been so generous.

But the challenges are great.

And I just felt it was time to tell the story and learn from it, if you would, and to inspire others, take up the torch.

AMNA NAWAZ: I noticed, even as we're sitting here, your eyes occasionally flick over to the photo and Jim's face.

What's it like for you to see that photo?

DIANE FOLEY: Oh, Jim was such a -- he was the oldest of our five children, a beloved son.

But he's challenged me.

He's challenged me, because I failed him, Amna.

I did.

Our government failed him.

We failed these young Americans, not just Jim, Steven Sotloff, Peter Kassig, and Kayla, as well as Luke Somers and Warren Weinstein were killed in that same time frame.

So we failed.

And we are learning.

President Obama fed up the Hostage Fusion Cell that still exists.

We have a brilliant current hostage special envoy at the State Department.

More than 100 people have come home since 2014, a lot of good things to celebrate.

But the challenge remains.

More and more countries are targeting our citizens.

And we're very challenged, as the Foley Foundation, as is our government, to handle it all.

AMNA NAWAZ: You open this book, Diane, with an absolutely astonishing moment, which is when you sit down in the same room across the table from one of the men who kidnapped your son and brutally tortured your son and had pled guilty to the role he played in your son's death.

And one of the first things you say to him as you sit down is: "Good morning.

You can call me Diane."

DIANE FOLEY: Yes.

Well... AMNA NAWAZ: What made you want to go sit down and talk to him?

DIANE FOLEY: A lot of things.

Jim would have talked to him.

Jim would have wanted to hear him out.

Jim had worked with a lot of disenfranchised young people like Alexanda, who was so vulnerable to all the radicalization.

But I also, as a mom, wanted to tell him who Jim was.

And I really wanted to be able to see him as a human being who had made some horrific choices.

And it was good.

It was good.

I was grateful that God gave me the strength to do it.

AMNA NAWAZ: You also write about yourself and your husband, John, at one point, and you say: "It is incredible, though, what you don't know about your own child.

Maybe it's the same for every parent, but it struck John and me years later that we didn't really know Jim all that well, not in his entirety, until after he was gone."

DIANE FOLEY: I know.

AMNA NAWAZ: What did you learn about your son?

DIANE FOLEY: So much.

Jim was our oldest.

And because we had four others, I was quite busy... (LAUGHTER) DIANE FOLEY: ... and with the younger ones and working part-time, and I loved my work as a nurse practitioner.

So, Jim, when he came home, wanted to interview us, wanted to know how we were.

What's up?

What's going on?

And really didn't share a lot about what he was up to.

He really didn't share a lot, I realized.

And it was really only after his death that I realized how many people he touched, how many lives he mentored.

I had no clue about anything, because Jim never talked about it, you know?

AMNA NAWAZ: You mentioned the foundation that now carries his name, the James Foley Foundation.

You have already changed how this U.S. government handles hostage affairs.

You advocate for the dozens of Americans who are still held hostage abroad right now.

But I should note, I see how hard you work.

Others who know this work see that your own family has asked you to slow down.

What is it that keeps you so devoted and so dedicated and moving forward every single day?

DIANE FOLEY: Well, I'm challenged by the needs that continue.

We have definitely improved as a government, but we have a long ways to go.

We have nation-states that are targeting our citizens now and wrongfully arresting them.

We have got to figure out how to deter this practice.

We must, because a lot of people are still suffering.

And it's still hard to get the attention for some of these families, even with the wrongful detention process.

It's rather opaque.

We're struggling, working with our government to try to figure out ways to help people understand where they are in the process and what is possible for the government, what is not, what we need third-party experts to help with.

Our government can't do everything.

So that's partly our role, trying to help families figure out how to get the attention they need to bring their loved one home.

AMNA NAWAZ: What do you think Jim would think of the work you're doing today?

DIANE FOLEY: I think he'd be doing some of that, to be honest, although I don't think he would have left his beloved journalism.

He believed in the power of journalism, and he really believed that we had to be in conflict zones, we had to bear witness.

He really believed in that.

So I think he'd be doing what he was doing, and I think he would want someone to be advocating for those who are targeted and held hostage.

AMNA NAWAZ: The book is "American Mother," co-written by Colum McCann and Diane Foley.

Diane, always a pleasure to have you here.

Thank you.

DIANE FOLEY: Thank you so much, Amna.