Story of the Kurds fits quite comfortably inside the missing piece of that large 'bad guys' puzzle.
Source of map:- Wikipedia
(Attribution) By PANONIAN - Own work, CC0, https://commons.wikimedia.org/w/index.php?curid=54996333
Kurds in Syria currently:
Syrian Kurds have strong disagreements with the Syrian National Council (political wing [of sorts] of FSA). Yet, as the YPG works in partnership with the US coalition, it also cooperates with FSA. The scenario isn't only an evidence of Kurdish-NATO connivance but a clear evidence that the Kurds will collude with any crook or cutthroat to achieve their political goal. Needless to mention, FSA carries an ideology identical to all AlQaeda groups including ISIL whom Kurds have been fighting. FSA has systematically served as a conduit for foreign arms and money to AlQaeda factions inside Syria and has been responsible for inflicting mass brutalities on Syrian civilians. Kurds have long been linked with US intelligence to promote ethnic dominance in the Kurdish region. From 2014 onward, they've been regularly providing feedback to US officials on the activities of Syrians and Iraqis. They are officially cooperating directly with FSA.
Image source: Quora
Taking up arms against ISIL is little or no reason to count on the Kurds as one of the groups that stand for the betterment of the Syrian Republic. Their ideological approach is perceptibly as destructive as AlQaeda's and their animosity towards the Syrian Government just as intense. Syrian Kurds have simplified the plan of foreign powers to dismember Syria, assisting to make the mess still messier. Presence of the Kurds has further popularized the plan of partitioning Syria.
They make up approximately 10% of the Syrian population. They have been claiming the Syrian northeast since end 2013 declaring it an autonomous zone. That was the time when ISIL fighters began proliferating across Syria and Iraq, getting stronger than their US financiers would appreciate. Washington was fully focused on curbing the strength and power of ISIL, retaining the terror group as a standby, but only strong enough to serve US interest. Back then, American officials thought little or nothing on forging an alliance with the Kurds and the zeal of Kurdish nationalism went largely unnoticed. It was as late as the fall of 2014 when the Kurds kicked out ISIL from Kobane, that they became adamant on "federalism in Rajova." PYD insists it isn't interested in an independent Kurdish state within Syria but acknowledges that it wants to be a part of "future democratic federal Syria." It rejects speculations that it's on Assad's side, asserting it's fighting Assad as well as ISIL. But there are regional differences within the Kurds which might, at some point, play to the advantage of the Syrian Government. Iraqi Kurds (KRG) are in no mood to support independence of Syrian Kurds as that could put them on a collusion course with Turkey; KRG isn't willing to take the risk. Even the Americans are wary on that issue. At present Washington is handling quite a balancing game, utilizing the support of the Kurds taming ISIL and simultaneously not going too far pampering the Kurds that could annoy Turkey. But hidden Western policy is more vividly exposed by retired diplomats who have been quite candid about their appreciation of Kurdish independence, namely citing the visit of Peter Galbraith and Bernard Kouchner to Qamishli in November 2016.
President Bashar al-Assad. Ara News, October 2016.
In October 2016, President Bashar al-Assad discarded the idea of "federalism" in Hasakah Governorate (northeast Syria) without a referendum as the majority in Hasakah are Arabs. It goes without saying that in an autonomous "Rojova" controlled by Kurds, ethnic discrimination and persecution of non-Kurds would be too rampant for the rule of justice to prevail. But all Kurdish movements stand staunchly for federalism, interpreting it as "end to the dictatorship of the Arab majority." You may recall, during Obama's regime federalism was 'plan B' among the suggestions of John Kerry for the break-up of Syria.
Kurdish fighters fire machine gun mounted on a truck with FSA flag, Kobane 2014. Daily Mail.
All Kurdish factions in Syria have abandoned waving the 2-green-star Syrian flag, replacing it with the Kurdish flag in the northeastern towns like Qamashli, Manjib, Afrin etc. The Kurdish National Council has rejected the 'Syrian Political Solution' issued by the UN in early March 2017 as it mentions of Syria as "one people," seen by the Kurds as an oversight on the aspect of "ethnic diversity."
Kurds celebrating nauroz in Qamishili, Hasakah Province, northern Syria, waving the Kurdish flag. Image: Ara News.
Kurds of ISIL:
May sound bizarre but it's real; it exists.
Paraphrasing below a quick summary from Foreign Affairs on the lengthy history of Kurdish extremism and its links to AlQaeda.
This aspect also explains why and how many Kurdish commanders at present are well acquainted with AlQaeda's tactical warfare. According to Kurdish officials, there are hundreds of Kurdish-ISIL sleeper agents either in KRG or within ISIL ranks.
Yes, it's worth reiterating that the participation of the Kurds in the Syrian war contributes generously to the dismemberment of the Syrian Arab Republic.