How can we explain the sudden appearance of ISIS in Iraq and its seemingly easy victories?

Many factors help explain this shocking development: Syrian and Iraqi government repression of their Sunni populations; the brilliant leadership of ISIS; Turkish and Qatari support; and the illegitimacy of a state created by the United States and its allies. Beyond these specifics, the Sunni Arabs, Shia Arabs and Kurds of Iraq all feel greater allegiance to each of their own communities than to the central government, which has struggled with weak allegiances since its creation in the aftermath of World War I and now, finally, is splitting apart.

Isn't it surprising that a large part of Iraq's Sunni population should choose the most extreme jihadi force as its voice, especially given its secular past under the Ba'ath regime?

Yes, it is surprising – and that is one of many recent surprises. It's also quite predictable that the Sunni population, once it learns what life is like under ISIS, will reject it. It now finds Islamism attractive; wait till it experiences more of it. The most spectacular example of this realization was Egypt in the years 2012-13, but we've also seen this phenomenon in Tunisia, Libya, Sudan and Iran.

What role does the Turkish government play in this conflict?

It's the primary backer of ISIS. Without Turkish support, ISIS would not be where it is. Qatar is important, too, as a major source of financial support, but Turkey provides more than that: arms, refuge, training and medical assistance. There are even reports of retired Turkish soldiers serving in ISIS.

But why should the Turkish government have any interest at all in encouraging problems along its own border?

Erdoğan had such close personal relations with Bashar al-Assad that he and his wife vacationed with the Assads. When the troubles began in early 2011, Erdoğan gave Assad (good) advice on how to respond. But Assad rejected Erdoğan's views and Erdoğan, who has a volatile personality, responded with great anger. Since then, Erdoğan has done everything to bring down the Assad regime, including support for ISIS.

The best of friends: 2009, when the Erdoğans and the Assads vacationed together in Turkey.

So it all boils down to the vanity of one man?

In large part, yes. Erdoğan dominates Turkish politics. Especially since the elections of 2011, he has done whatever he wishes.

Do you think that President Obama – or, for that matter, anyone else who holds power – has a plan to stop the jihadi forces in Iraq and Syria?

I see no plan. Western governments are sending arms, hoping that these go to the better – or less worse – elements in Syria, but that hardly constitutes a plan.

Some people recommend arming the Kurds, the most secular and moderate power in Syria. Is this option being considered in Washington?

Yes, it is a good idea and has been around for some years. But it has never been official American policy and would require a major shift...