My Damascene friend, Abed, and I often talk about regret. Do I regret the Iraq War? Does he regret the Syrian revolution? I served as a Marine in Iraq, fighting in places like Haditha and Fallujah. Abed took to the streets in 2011, participating in the pivotal Friday of Rage and Friday of Steadfastness protests, which helped start the insurrection against the dictator, Bashar al-Assad. Over nearly a year of friendship, we’ve had this conversation countless times, late at a café along Muhtar Pasa Bulvari, in Gaziantep, a city along the Turkish-Syrian border, or with our wives over dinner just off the Istiklal, in Istanbul. For a while, I thought there was a difference between us: my war was over. His continued, right across the border. Now that distinction feels less and less true.

The sacking of Mosul, Tikrit, and other cities by the Islamic State in Iraq and al-Sham doesn’t seem, at first glance, to be a chapter in either of our wars. It isn’t part of the Iraq War, at least not the one that I fought in. It isn’t part of the Syrian civil war, at least not the one being fought in Abed’s home. This conflict’s murky categorization has kept ISIS’s ambition to establish a caliphate straddling present-day Iraq and Syria largely from popular consciousness.

A few days before I met Abed, on September 19, 2013, I travelled to the Turkish border crossing in Kilis. My visit coincided with the day ISIS seized the city of Azaz from the Free Syrian Army’s Northern Storm Brigade, just three kilometres away. That afternoon, smoke from the embattled city corkscrewed upward along a flat, parched horizon of dust and sagebrush. On my second visit, I travelled to the same crossing point with Abed and a few of his colleagues from a local research organization. The smoke had cleared, but the crossing point was choked with refugees. Spread along the side of the D-850, a highway that once brought wealthy Syrians from Aleppo into Gaziantep for shopping trips, whole families from Azaz squatted with their possessions packed in flimsy suitcases. Seeing this, it seemed irrefutable that ISIS, although characterized as a rebel group in the Syrian civil war, did not consider the toppling of the Assad régime to be its primary objective. If it had, it wouldn’t have wasted resources seizing Azaz, a city held by the rebels since March, 2012. ISIS’s war wasn’t part of the revolution. It was a conquest all its own.

At times, I’ve heard Abed say that he regrets his revolution and he wishes that he—and, by implication, his generation—had never taken to the streets. At other times, I’ve heard him say he doesn’t: that the struggle isn’t over, and any chance to live in a free society is worth the suffering. Like me, he wrestles with the good and the bad, the duality within the defining political and emotional event of his life.

I’ve often been asked if I regret fighting in the Iraq War. I don’t. As an American of a certain age at a time of war, I had a choice to make: whether I would participate. What I regret isn’t my choice but rather that our political leaders couldn’t steer a course clear of war or manage a quicker peace. In the revolution’s early days, Abed’s choice was similar. During a time of change, would he choose to be an agent of change? Would he participate? I’ve always admired him for his involvement as an activist, but that participation has come at a severe cost. He is now wanted by the Assad régime for his role in the revolution, and he can’t return home. He may never return.

Since January, the outlook from Abed’s home, and from where I served, has been bleak. ISIS has seized huge swaths of territory and taken over Syria’s Ar-Raqqah governorate, as well as key cities in the American war in Iraq such as Fallujah and Ramadi. The rapidity of these advances has awed much of the international community. The success of ISIS can be attributed to many factors: the corruption and inefficacy of the Free Syrian Army, the Maliki government’s refusal to integrate Sunnis into the fabric of political life, and the lack of a residual U.S. force. Fundamentally, these factors can be reduced to one: a power vacuum.

That extremists would step into a power vacuum is no surprise. It happened with the Taliban in the nineteen-nineties and with Al Qaeda in Iraq in the past decade. In this part of the world, extremism is not a fait accompli. It was brought about by a certain set of conditions—lawlessness, sectarian violence, corruption. These create fertile ground for radical ideologies to take root. All these negative strains currently exist within Iraq and Syria. For instance, Abu Bakr al-Baghdadi, the head of ISIS, fought against the U.S. in the Iraq War, rising to become the chief of Al Qaeda in Iraq in May, 2010. In 2011, when Abed and other activists took to the streets across Syria, Abu Bakr’s organization appeared to be in its final throes. Then, in a collapsing Syria, it was offered the exact opportunity it needed. Just as the U.S. invasion of Iraq created a vacuum filled by international jihadis, so, too, has the democratically minded Syrian revolution. The convergence of the conflict in Syria with the conflict in Iraq has, strangely, made Abed and me veterans of the same war. And our wars each devolved into disasters for the same reason: by trying to unleash sweeping change in the region, we created the conditions for extremists to rise.

It seems fitting that the two of us, an American Marine and a Syrian activist, would try to understand the ascent of ISIS through each other. We often speak about years ago, when our causes were new. I’ve told Abed about witnessing the first Iraqi elections just after I’d lost friends in Fallujah—how it felt to see old men and housewives departing the polls with their index fingers stained by purple ink. Abed has told me of the pride he felt in seeing his countrymen stand up to the régime that had bullied them all his life.

Abed comes from a line of poets, and he shared “Take Me,” a poem he composed on December 9, 2011, the Friday of the Dignity Strike, during those heady early days:

I’ve taken my decision, put my olives and bread in the baskets

and stay awake praying for me Mother as long as the moon is up

I am lost for words to express

my overwhelming happiness to have an appointment with history

while carrying with me water for the rebels.

A few days ago, I was talking to Abed about this poem, what it meant to him, whether he still felt the same. “Back then, I was coordinating the protests in Damascus and the rebels were seizing ground in the countryside,” he said. ”All of us were bound by this platonic love of freedom. We felt like we were making history.”

“Do you think there’s some young member of ISIS marching to Baghdad now, glamorizing his appointment with history?” I asked.

“Sadly, it’s something we all have in common.”

Photograph by Militant Web site/AP.