We obviously don't want to cause problems for the Afghan government, President Hamid Karzai and the Afghan people. In fact, we want them to support our efforts on their behalf and not see us as unwelcome occupiers.

Progress in Iraq has always been about teams of people and teams of teams - and ultimately about young men and women, Iraqi as well as people from the coalition.

In Afghanistan you are not rebuilding, you are building. There is very limited infrastructure and extreme terrain, with deserts in the south and mountains so high in some areas that helicopters don't even fly well at a certain altitude because the air becomes so thin. The country has a serious problem of illiteracy, especially after so many years of war and Taliban rule.

ISIS is on its way to defeat but terrorism threat persists.

Afghanistan has other enormous challenges as well, including a political system that is still very much developing, although there has been some progress in the past several years.

Al-Qaida in particular remains dangerous, and there [in Iraq] is some residual militia and special group presence. There are still between 20 and 30 attacks per day, still periodic car bombs and still loss of innocent civilians.

US Ambassador to Iraq Ryan Crocker and I have repeatedly sought to emphasize that the progress in Iraq is fragile and also, possibly, reversible.