The present strategy of the US for defeat of IS is ultimately dependent on the Turks. Turkey is the main pathway through which IS receives recruits of both sexes and the main pathway through which IS continues to export oil to raise money. Erdogan's Turkey has until very recently barred the US from the use against IS of air bases built and maintained by the US for NATO. These bases are at Incirlik, Diyarbakir, and Batman.
Retired USMC general John Allen has arrived at an agreement with Erdogan for use of these bases for surveillance, attack and SAR purposes in the war against IS. This will be a great convenience to the US air forces.
The problem with this deal is that Turkey and the US have different expectations and goals in this arrangement.
The US wants the bases for the IS war.
The Turks want to facilitate the downfall of the present Syrian government in order to advance the cause of Sunni triumphalism in the Levant. In this, they are complicit with Saudi Arabia and other Sunni moneyed parties in the Gulf. The prospect of a Syria dominated by a Nusra Front led government does not bother Erdogan at all. He has much the same result in mind for Turkey if he can only get enough seats in parliament to change the pesky constitution with its elements of Kemalist secularism. He also must complete his purge of the officer corps of the Turkish armed forces who remain a threat while brooding over the present government of their country.
The Turks also want the US to help them bomb the Kurds (ALL THE KURDS) into submission or extinction, whichever comes first. To this end the Turks will use their own forces and to extent that they can persuade, the forces of the United States and the Europeans. the "allied" Arab air forces have little more than a symbolic political value in this.
For the United States, Turkey's desire to crush Kurdish nationalism is a major problem. The notion that the Pesh Merga, YDP and PKK Kurds are indifferent to each others' fates is an example of the kind of ignorant magical thinking that has run American policy in the ME since the neocons and R2P "crowds" have come to be dominant. In fact the Kurds despite their political and tribal differences are one people. If the United States is complicit in attacks on Kurdish fighters of any kind, it will risk with a high probability of occurrence the loss of the Kurdish ally.
I have been increasingly inclined to reluctantly accept the notion that the US should fight IS directly on the ground and in the air with its own forces and without regard for Arab "allies," not because the jihadis are an existential threat to the US but, rather because they menace civilized life in the Islamic World and across the rest of the world as well. In this context the obstacles presented by Erdogan's policies and crypto alliance with the Islamists are an obstacle to any future destruction of the Islamic State's caliphate. Without true Turkish cooperation victory over the IS phenomenon is not possible and the US should not attempt it. Turkey is IS's de facto protector.
The destruction of IS and Nusra would not mean that future jihadi movements would not someday arise, but such destruction would win time, and that would be enough. pl
PS Marcus says he has rejected the world and will not return but adds that I can use his image as an emblem of my musings.