Pepe Escobar has chronicled the beginning of the Syrian conflict: Assad agreed on a pipeline route with the leaders of both Iraq and Iran. thing of it is, Turkey and Qatar had a keen interest in a competing route that - potentially - would run through a post-Assad Syria. naturally, the early sponsors of the famous "Free Syria Army" were Turkey and the Gulf Monarchies (U.S. allies, hey !). but Syria's religious minorities - Christians, Alawites, Yezidis, etc - knew what these orgs were about - the "moderate al-Qaeda factions" and, later, the ISIS golem - and they backed Assad, a *secular* dictator, out of a natural sense of self-preservation.
since then, Russia has entered the mix, bombing Salafist mercenaries regardless of affiliation. and, sure, taking out ISIS supply routes from Turkey (and, presumably, the routes used by ISIS to send Erdogan oil). and since Turkey has been quietly annexing Syrian territory since the conflict began, a "Russian incursion" is not inconceivable. in any case, this would be a good opportunity for Russia to resupply the PKK. Erdogan, after all, is killing his own people in Southeastern Turkey / unless he considers the Kurds, like the poor Armenians before, not his people at all, but a pestilence to be eradicated ..