Tens of thousands of Yazidis, the largely Iraqi ethno-religious minority fleeing the forces of the Islamic State, are slowly reaching safe havens after a week-long crisis that prompted U.S. military airstrikes on positions held by the Islamic State's emboldened fighters.

They have endured horrors. Dozens of children died of thirst and hunger on the arid peaks of Mount Sinjar, where many Yazidis had run a week ago after the jihadists overran nearby Yazidi towns, executing men and enslaving women as concubines, according to some reports. The journey off the mountain has been arduous and deadly. The Associated Press reports some exhausted mothers "abandoned living babies."

As explained here, the Sunni extremists consider the Yazidis apostates and therefore deserving of such brutality.

My colleague Liz Sly witnessed part of the exodus, as hundreds of sun-burned and blistered Yazidis poured across the border with Syria: "Hungry, thirsty and tired, they limped across a narrow bridge spanning the Tigris on the Iraqi-Syrian border hauling their few belongings, some of them barefoot, others in sleeping clothes because they ran for their lives at night."

It's unclear to what extent U.S. airstrikes, combined with humanitarian drops of food and water supplies, directly aided the Yazidis who survived their difficult march toward safety. What has proven more essential has been the role of Kurdish militias on the ground who have helped secure corridors of escape at least for some Yazidis. (The Yazidis are largely Kurdish speaking.)

This initiative doesn't just involve the pesh merga affiliated with the government of Iraqi Kurdistan, but a whole constellation of Kurdish units drawn from Turkey, Syria, Iraq and Iran. One of the main organizations in the counteroffensive against the Islamic State is the Turkish-based Kurdistan Workers' Party, known by its acronym, PKK. Because of its history of militancy and violence in Turkey, it is still recognized by the U.S. State Department as a terrorist organization.

That reality echoes awkwardly with the present. Last week, as my colleague Loveday Morris reported, the PKK called for collaboration between an alphabet soup of oft-fractious Kurdish factions. One of the main outfits safeguarding Yazidi escape routes into Syria and retrieving the refugees at the border is the YPG, the armed wing of the Syrian Kurdish PYD party, which is itself an offshoot of the PKK. The YPG has fought both Islamist rebels in Syria, as well as the forces of embattled Syrian President Bashar al-Assad. Portraits of Abdullah Ocalan, the jailed founder of the PKK and a hero to many Kurdish nationalists, are ubiquitous in YPG camps, reports Al-Monitor.

The PKK emerged as a Marxist-Leninist guerrilla organization in the 1970s, seeking Kurdish independence from a Turkish state that had long suppressed the Kurdish identity and language. It employed terror tactics by the 1980s, carrying out bombing attacks and kidnappings. Its decades-old insurgency has claimed some 40,000 lives, though in recent years the PKK has found ground for rapprochement with Ankara and has ceased hostilities. A peace deal led to the withdrawal of PKK forces to camps in Iraqi Kurdistan.

Now, PKK fighters are manning the front line by the Iraqi city of Kirkuk. Aided by U.S. airstrikes on Islamic State positions, they also helped take back the key town of Makhmour from the Islamic State on Monday.

Ideologically, the PKK and its offshoots are not religiously motivated. Women fight alongside men; there's been a recent fascination among Western journalists with the prevalence of female units in the YPG. Some in the United States are lobbying for the PKK to be de-listed, but that act would require a political will that at present is lacking and risks irking Turkey. Meanwhile, it's already apparent the United States is arming two other Iraqi Kurdish factions, the PUK and KDP, which are nevertheless categorized as "Tier III" terror organizations by the State Department.

The irony of the moment is profound: The United States is essentially aiding a "terrorist" group to fight other militants in a country it occupied for almost a decade. It highlights the many conundrums facing American policy makers. To what extent should the Kurds be given free rein now? Should the United States abandon its longstanding support for a federal, inclusive Iraqi state? And how far will the United States go as the PKK and other Kurdish militia take the fight to the Islamic State?