GEOFF BENNETT: Already scarred by decades of war, Afghanistan became the center of America's response to 9/11 after the Taliban harbored the men who planned the attacks.

Special correspondent Leila Molana-Allen and videographer Eric O'Connor hear from three men who fought that war and still carry it with them.

MOHAMMED, Former Afghan National Army Special Forces Soldier (through translator): After all that fighting, everything we lost, our friends, we lost everything we did for this country.

And that is a trauma for the rest of our life.

Everything was just for nothing.

LEILA MOLANA-ALLEN: Mohammed, whose name we have changed to protect him, grew up amid America's forever war in Afghanistan.

He believed in the promise of a new Afghanistan and became a soldier to fight for it.

As a member of the Afghan Special Forces, he was trained by U.S.

Marines and fought alongside the Green Berets on secret raid missions, pursuing high-level Taliban and ISIS targets from 2019 to 2021.

MOHAMMED (through translator): We had a very good friendship.

We had very good instructors.

And we weren't thinking that we're Afghan or they're U.S.

forces.

We were like the same people, the same blood, the same idea that we were fighting for humanity.

LEILA MOLANA-ALLEN: But, in 2021, they were told to surrender their weapons and go home.

The Taliban were now in charge.

Suddenly, he became the high-level target for his work with U.S.

forces.

It soon became clear the U.S.

military couldn't or wouldn't get him out.

MOHAMMED (through translator): America had promised that the people fighting with us, we will stand up for them.

I thought, what did we do wrong that they would abandon these people that they fought alongside?

LEILA MOLANA-ALLEN: Mohammed is at such high risk that, even though we're in the same city, we can't visit him in case we're followed.

He tells me he's being hunted.

Every few days, he hears news of the execution or arrest of former brothers in arms.

He says, no matter how strong they are, he knows every human being eventually breaks under torture and could reveal what they know.

So, last month, your friend was executed by the Taliban who was a former soldier.

MOHAMMED (through translator): Yes.

LEILA MOLANA-ALLEN: You're living in hiding.

You know people are searching for you.

What is your daily life like?

MOHAMMED (through translator): Our life now is just waiting.

When will they find you?

When will be your last day in this world?

LEILA MOLANA-ALLEN: He hasn't seen a family member or friend in five years.

He can't put them in danger.

The only people he does see are a secret network of former soldiers who help men like him move between safe houses.

So you're moving every couple of weeks.

MOHAMMED (through translator): Yes.

LEILA MOLANA-ALLEN: What's it like to be constantly on the run?

MOHAMMED (through translator): You cannot call that a life.

It's really hard, like you're a criminal or something, like everyone is following you.

LEILA MOLANA-ALLEN: In a quiet corner of Kabul, behind high stone walls marked by the centuries, stands a garden of memories.

The Kabre Gora, the 19th century name for foreigner, holds the names and remains of foreign fighters killed here over centuries of war, Americans, British, Canadians, Russians, French, Germans, Poles, en Chinese, a graveyard for the human beings who lost their lives in the country famously called the graveyard of empires.

Combat medic Bryan Rippee is not there.

He made it home after four tours in Afghanistan, serving with the elite 75th Ranger Regiment from 2009 to 2012.

Many of his comrades did not.

One of a generation of volunteers driven to serve by 9/11, Bryan says he only really came to understand what the war was for once he was already there fighting it.

BRYAN RIPPEE, Former U.S.

Army Combat Medic: Nine-eleven really changed the discourse about what it meant to serve and how important it was.

When I started to deploy to Afghanistan, our mission had really shifted focus from being finding al-Qaida and the folks that had done 9/11 and planned it and executed it to being one where we were fighting the Taliban.

What is the tie-in between these seemingly farmers and relatively poor people that were going and doing these missions to go after, what is their connection to 9/11?

LEILA MOLANA-ALLEN: While on a night mission on his first tour, an apparent success went horribly wrong when a Ranger stepped on an improvised explosive device the Taliban had placed on a bridge.

BRYAN RIPPEE: Suddenly there's a giant explosion, and then everything is covered in dust.

And so you're running through a dust storm, essentially.

And me, as the medic, I'm not really sure what I'm running towards.

What sticks with me to this day is just the chaos of it all, combat-tested folks, combat leaders looking very frazzled, seeming very desperate and a little panicked.

That's just not something I had seen to that point in my career.

LEILA MOLANA-ALLEN: Saving many others, Bryan only discovered later that the man who stepped on the IED was his closest friend.

BRYAN RIPPEE: I lost a really, really good friend of mine.

My oldest son's middle name is Roberto, after Roberto Sanchez, who died that day.

The hardest part was getting back to our tent and seeing his empty bunk.

It's like losing a brother.

As the years go by, I have since gone to college, started my career, gotten married, had a couple of kids.

I always wonder what he would have gone on to do.

Would our kids have played together?

LEILA MOLANA-ALLEN: That same year, Bryan pulled a pilot near death from the wreckage of a helicopter crash that killed four other crew members.

The privilege of saving a life is one he won't forget.

BRYAN RIPPEE: I think about that guy a lot, because I'm like, hey, that really to me is the culmination of all that training and all the risk that you assume to be on these missions all the time.

It's just -- it's the opportunity to save one life and to feel like you saved it.

LEILA MOLANA-ALLEN: Bryan was awarded Special Operations Medic of the Year for his valor in 2009 for both those operations.

To this day, he struggles with the idea that he gained so much from his service personally, while others suffered incalculable loss.

BRYAN RIPPEE: I made it out of the war and kind of turned that into a life for myself.

A lot of folks I know didn't, and countless others, Afghan folks, multigenerational conflict for the Afghans.

LEILA MOLANA-ALLEN: Every inch of this vast country bears the memories and scars of that conflict.

During the war, this road was one of the most dangerous in the country.

It was a critical supply route for international forces, making it a frequent target for improvised explosive devices.

And these high mountain passes gave the Taliban natural hiding places from which to launch ambushes.

Today, Mujahir Farahi sits in an air conditioned office in Kabul as a deputy minister in the Ministry of Information and Culture.

But he remembers those days, hidden in the high mountains, waiting to attack.

MUJAHIR FARAHI, Former Taliban Fighter (through translator): Of course, in the beginning, fighting the Americans was tough.

But slowly, with time, the mujahideen used diverse tactics against them.

They used things that could be made at home and inside the country, like land mines or other weapons they made themselves.

Suicide attacks proved effective.

LEILA MOLANA-ALLEN: As a Taliban mujahid, he fought the United States in Afghanistan for 20 long years.

MUJAHIR FARAHI (through translator): Yes, many of our friends were martyred and injured, some in front of our eyes.

I myself was injured.

Luckily, the enemy wasn't able to catch me.

LEILA MOLANA-ALLEN: To him, their victory and resulting control of the country is the inevitable outcome of their decades of commitment to jihad.

MUJAHIR FARAHI (through translator): When the Americans started the war and Bush announced the occupation of Afghanistan, it was the worst day.

But after 20 years of fighting to remove the occupiers, we entered the cities and the whole country was freed.

This was medicine and a resolution for that 20 years of fighting and exhaustion.

LEILA MOLANA-ALLEN: He wants the United States to accept the outcome it chose, lift sanctions, and agree to full diplomatic and trade relations with Taliban-run Afghanistan.

MUJAHIR FARAHI (through translator): All of this was made clear in the agreement in Doha that there would be no more meddling into Afghanistan's internal issues and no economic restrictions.

When America doesn't hold to their side of the deal like this, we feel they are taking revenge on Afghanistan for the past.

LEILA MOLANA-ALLEN: It's a war that left Mohammed and millions of other Afghans, now deprived of their personal safety and their rights, wondering what happened to the safer Afghanistan and safer world America promised and whether it might have been better if they'd never come at all.

Are you proud of the work you did alongside America?

MOHAMMED (through translator): Yes, definitely.

But now these are the same people, the same leaders back in power.

So why did you come to Afghanistan and fight for 20 years and spend billions of dollars and lose thousands of your best people?

LEILA MOLANA-ALLEN: When Bryan and his buddies think about the risks they took and the sacrifices they made, Bryan says he's consumed by emptiness.

BRYAN RIPPEE: Nine-eleven led to this decades-long war in Afghanistan.

I don't think that the blood and treasure that we spent in Afghanistan for several decades has changed the security of America for the better in any measurable way.

A lot of folks my age that served in the war look at Afghanistan now and they think, OK, the Taliban's in control there, which was like the very thing a lot of us were willing to die to prevent.

It truly feels like we went there and spent years of our lives fighting for something that became completely inconsequential.

LEILA MOLANA-ALLEN: A country forever changed, but somehow right back where it started, with only blood, betrayal, and bitterness to show for it.

For the "PBS News Hour," I'm Leila Molana-Allen in Kabul, Afghanistan.