The capture of the strategic northern border town of Tal Abyad from Islamic State (IS) is the latest in a string of gains by the dominant Kurdish militia in Syria, the YPG, and its political branch, the PYD, across the north of the country since 2011.
In January, their fighters grabbed world attention when they drove IS out of Kobane, another border town further east.
Now, the YPG, working with some Free Syrian Army-aligned rebels, and backed by US-led coalition air strikes, have taken control of Tal Abyad, with its ethnically mixed population, that had been held by IS since last year.
The YPG's victory in Kobane was symbolically significant, but Tal Abyad offers far more strategic value.
Long-term control of Tal Abyad would further the YPG's goal of connecting the non-contiguous zones of territory it holds across northern Syria, which it organises into three "cantons": Afrin (north-west of Aleppo); Kobane (west of Tal Abyad); and al-Jazira (north-east Hasakeh province).
If the YPG is able to hold Tal Abyad and use it to connect Kobane to al-Jazira, it will increase its strategic value to the US-led anti-IS coalition and will empower its self-governance structures in predominately Kurdish north-eastern Syria.
Tal Abyad is important to the anti-IS coalition because the town has long served as a key IS supply route, and a crossing point for foreign fighters seeking to join IS in Raqqa, the group's de facto capital.
There are few organised, trained and willing forces in Syria that the anti-IS coalition can rely on as a ground partner in its campaign in Syria.
Moreover, Turkey has been reluctant to fully co-operate with the coalition, instead tolerating a porous border with Syria that has, in the words of one US official, created a "permissive environment" for jihadists.
While Tal Abyad has been under firm IS control, for instance, Turkey has continued to allow some supplies to cross in from the Turkish border town of Akcakale, including sacks of fertiliser that contain ammonium nitrate used by IS to build explosives.
Turkey's vacillation stems in part from its prioritisation of toppling Syrian President Bashar al-Assad over fighting IS, and in part from its fear of the YPG. It views the latter as equivalent to the Kurdistan Worker's Party (PKK), which it treats as a "terrorist" organisation.
The PKK - also labelled "terrorist" by Western governments - has been waging a 30-year insurgency for self-rule in eastern Turkey, a key Western ally. The unrest has killed more than 40,000 people, mostly Kurds.
In this context, the YPG shines as a willing and able coalition ground partner against IS in Syria.
The group shares the PKK's secular, leftist-rooted ideology, which stands in stark contrast to the various shades of Islamist identity adopted by most other major Syrian opposition groups.
YPG fighters, many of whom have been well-trained by the PKK, have proven their ability to take on IS not only in Syria, but also in parts of north-western Iraq.
Brig Gen Thomas Weidley, the chief-of-staff of the anti-IS coalition, specifically praised the YPG on Monday, saying: "Since fall 2014, Kurdish forces in both Iraq and Syria, enabled by the coalition, have only taken territory from Daesh [a pejorative term for IS], never ceding it."
Yet, despite this impassioned praise in the wake of victory, coalition countries continue to at times treat the PYD/YPG as a pariah.
Coalition countries have, with few exceptions, stopped short of openly arming the YPG, in part because it is affiliated with the PKK.
Although the US-led coalition is co-ordinating air strikes in Syria with the YPG, Washington has refused to give the civilian PYD leader, Saleh Muslim, a visa to the US.
This inconsistent policy limits the PYD/YPG's ability to diversify its international backers and, in effect, keeps it reliant on pacts with Iran and the Assad regime.
Quid pro quo
The PYD/YPG's rapid rise in Kurdish-majority parts of northern Syria starting in 2011 was in part owed to a deal with the Syrian regime, which tolerated PYD control of some Kurdish areas in exchange for PYD repression of Kurdish anti-government demonstrations.
A non-aggression pact with the regime - based on pragmatism rather than shared sympathies - remains mostly in force today, and has allowed the YPG to focus its efforts on fighting jihadist groups.
But that association has cost the YPG credibility in the eyes of other Syrian opposition groups, anti-regime Kurds, and coalition countries that want to see Assad fall.
For now, the YPG only benefits from air strikes and intelligence when and where the coalition's goals overlap with its own.
But its role in pushing IS out of Tal Abyad, and its collaboration with certain Free Syrian Army rebels in that fight, may encourage coalition countries to engage the group more directly.
If managed well, this could have the effect of reducing its dependence on institutions controlled by the Syrian regime.
Ultimately, the key to normalising the coalition's relationship with the YPG would be progress in the Turkey-PKK peace process, which would allow Turkey - and thus its Western allies - to engage the PYD/YPG with greater flexibility.
Cale Salih is a Visiting Fellow at the European Council on Foreign Relations. Follow her @callysally