I did a week-long assessment in 2005 at (then Defense Secretary Donald) Rumsfeld's request. Following our return, I told him that Afghanistan was going to be the longest campaign of what we then termed "the long war."

Iran, as we have already discussed, has carried out very, very harmful activities inside Iraq. Funding, trainings, arming and, in some cases, even directing the activities of the special groups associated with the Jaish al-Mahdi and the Sadr Militia.

Even the Interior Ministry in Riyadh was hit. Since then, the Saudis have employed a very intelligent and comprehensive approach to counter al-Qaida, including precise operations based on good intelligence, changes in their corrections facilities, superb strategic communications programs and a host of other initiatives - all of which, together, have helped Saudi Arabia achieve impressive results in their fight against extremists.

If you look at casualties, you find countries that had much higher loss rates per capita than the US. Denmark comes to mind, the United Kingdom, they have suffered heavy losses at various points, the Germans as well.

The president and I sat down in the Oval Office, and he expressed very clearly that what he wants from me is my best professional military advice.

Let's remember that the reason we are there is that we have vital interests in Afghanistan, hugely important national interests, as do the other countries involved.

The Islamic State fighters in Mosul are dead men walking and I think they increasingly know it.