When you ride in a windowless armored vehicle, you lose track of time and distance to the point of disorientation. So when our Stryker unit rumbled south on Highway 1 from Mosul to begin surge operations in Baghdad in 2006, I stood up in a hatch, hotwired a megaphone and blasted Pink Floyd from an iPod. As attack helicopters flew ahead to scout for potential bombs, I listened to David Gilmour belt out Time – a song about wasting the moments we are given.

This week, two and a half years after the last American forces left Iraq, the al-Qaida splinter group Islamic State of Iraq and Syria (Isis) traveled the same route down Highway 1 after taking Mosul, attacked the strategic oil refining town of Baiji, seized Tikrit and now threaten Samara – a city 132km from the capital. With the western route through Anbar Province secured, both paths now point the militants toward Baghdad as Presidents Obama and Maliki mull airstrikes.

As with the fall of Fallujah to Isis earlier this year, Iraq veterans are once again left to wonder if the shorn lives and limbs are worth the cost of a troubled nation spiraling, once again, into chaos. Did I waste my time? Did my buddies die in vain? These are the questions that many of the 2.5m Americans who saw combat are asking themselves. On Facebook, many of my Army friends have voiced their frustration over the Iraqi Army – once trained by us – after they abandoned their positions in the face of a relatively tiny force.

But many of my fellow veterans have missed an important point: this war was always about Iraqis, not American troops. Since the 2003 invasion, violence along sectarian fault lines threatened the stability of the nation as US troops fought, and died, to create strategic and diplomatic space for a stable government. We could only triage on the ground – it was up to the government in Baghdad to create permanent solutions. And Nouri al-Maliki's brutal sectarian policies ruptured US gains since the moment we began leaving in earnest.

Iraq veterans should not beat themselves up by attaching their ideas of sacrifice – of worth to a nation – to that broken government we left behind. We did what was asked of us. We held up our end of the bargain. Maliki did not, and many Iraqi troops similarly betrayed their own people when they chose not stand between extremists and their own countrymen. It has always been their fight, but that is especially true now. The American public and its Congress allowed the war to happen, and it was the US military's job to help Maliki create the security necessary to establish a functional government. The march of Isis to Baghdad shows how spectacularly they have failed.

Young Iraqi men and women have to figure out a way to hold the line. Not us. We have to think about measuring the worthiness of sacrifice here at home.

Many veterans back in America choose a less dangerous way to get something out of the life our fallen comrades have given us. Some help their neighbors clean up after natural disasters or strive to be community leaders. Countless veterans teach their children that serving others is the best thing you can do in life.

But I know it's hard to do that. Our lives are defined by moments in combat that will take decades to understand. And while many veterans are succeeding here at home, there are significant challenges, like post-traumatic stress, a volatile job market and a government that has failed in its charge to care for us. These issues will impact our future far more than members of Isis hijacking gun trucks and seizing police stations.

As a former soldier, I'm frustrated at the strategic losses strung together down Highway 1. As a human being, I feel some guilt that I was part of a force that dismantled the Iraqi state and could not find a way to rebuild it. I want Iraq to be a place of peace that I can visit with my children one day, and tell them about the men who died so they could be born. But it doesn't look like that will be possible – not in the near future anyway.

This month, I watched one of my best Army friends graduate from the FDNY Academy. Our job overseas was rather simple: maneuver and destroy the enemy in close combat. We used to go house-to-house to kill insurgents manning rooftop fighting positions. Under the threat of a different fire, in New York, my buddy will now look to save lives rather than end them. His past hardships will not be in vain.



As the months and years in Iraq become smaller parts of our existence, it becomes crucial that we look around at home to legitimize the sacrifices of our comrades who paid with their lives, limbs and minds. We need to define our own worth – instead of allowing the political whims of a foreign country to do it for us. A lyric from Pink Floyd's Time warns us of that futility: And you run and you run, to catch up with the sun, but it's sinking.

• From another veteran on Guardian US opinion today: I remember Mosul, but Iraq 3.0 is what happens when you exit a war early | By Colby Buzzell