The fact to the matter is, we never developed a comprehensive strategy to deal with radical Islam. And the 9/11 commission said one of the things we must do is develop a global alliance to combat it.

This radical Islam is a religious-based ideology. And you actually have to, when you deal with the ideology, you have to attack it on that basis.

It's not that I can't be fooled, but I'm not fooled often.

Fighting forces, particularly ground forces, have to operate on the basis of unit cohesion.

What did we want out of Iraq? We wanted a country that was stable and secure, that elected its own government, that was not going to be a threat to its neighbors and also was capable of protecting and defending itself. That was our objective in Iraq.

Air power will not defeat ISIS. It has not been able to deny ISIS freedom of maneuver and the ability to attack at will.

Economically, ISIS is making money every day on the black market with their oil fields. But they are also putting money in banks. We know where those banks are. We should go after the banks and the facilitators using them.

Qatar has funded and helped arm ISIS. They also, as we all know, fund Hamas. That's got to stop. And we've got to use our pressure against that country to knock that stuff off.

If you're going to maintain true authorities over a subordinate organization, you have to have some control over policy formulation of that organization and also the resources that are applied to it.

We have a sufficient political class, and the military doesn't have to get involved in high national office. The days of doing that, post-Civil War and post-World War II, are gone.

I'm not in a position to go back into public service.

ISIS is at war with America, but America is not at war with ISIS - not the president, nor the Congress, and certainly not the American people.

The success of ISIS is largely tied to the safe haven it has in Syria.

The fact that we walked away from the Middle East, as distasteful as it was for us to stay involved and prevent wars, based on our long involvement there, we have helped to create and provide a foundation. Obviously for ISIS and also for the absolute barbarianism and human catastrophe that Assad impacted on his people.

Russia, their number one client in the Middle East is Syria; that is their foothold in the Middle East. They want to have influence there.

Most people who aspire to be president don't have a foreign policy and national security background. The exception was certainly Hillary Clinton.

'Duty' is a refreshingly honest memoir and a moving one. Mr. Gates scrupulously identifies his flaws and mistakes: He waited too long, for example, for the military bureaucracy to fix critical supply issues like the drones needed in Iraq and took three years to replace a dysfunctional command structure in Afghanistan.

Only four secretaries of defense served longer than Robert M. Gates. Many others were as dedicated; many sacrificed a great deal. Alone among them all, however, Mr. Gates had the task of turning around two wars that the U.S. was losing.

Since 1989, we have been deploying on an average of every 18 months.

I have decorated soldiers for heroism before, and it was always such an honor to do it.

The Pentagon is actually a 10-story building, five up and five down.

Radical Islamists spread from Western Africa through the Middle East, all the way to South Asia to sub-Indian continent.

Very unusual in an insurgency to have absolutely no political agenda other than to return to power. Most insurgents have a political side to them.

By the end of 2008, clearly the Al Qaeda and Sunni insurgency had been relatively stabilized. And in the Al Qaeda's mind, they were defeated.