In 2005, troop levels in Iraq were increased to numbers nearly equal to the 2007 surge — twice. But the effects were not as durable because large segments of the Sunni population were still providing sanctuary to insurgents, and Iraq’s security forces were not sufficiently capable or large enough.

The decision to conduct a surge came out of an interagency review in the fall of 2006. By mid-December, as I was leaving the Pentagon, there was a rough consensus in the Defense Department that deploying additional combat brigades to Iraq was the right step. Some military leaders raised reasonable questions about the potential effectiveness of a surge, in part because of a correct concern that military power alone could not solve Iraq’s problems. I agreed, and emphasized that a military surge would need to be accompanied by effective diplomatic and economic “surges” from other departments and agencies of the American government, and by considerably greater progress from Iraq’s elected leaders.

During my last weeks in office, I recommended to President Bush that he consider Gen. David Petraeus as commander of coalition forces in Iraq, as General Casey’s tour was coming to an end. General Petraeus and his deputy, Gen. Ray Odierno, had the experience and skill to recognize and exploit the seismic shifts that were taking place in Iraq’s political landscape. And United States troops had the courage to win the alliance of Iraq’s people against a common enemy — and the benevolence to win their friendship.

At the critical moment — a moment when the Iraqis were able and willing to be part of the surge with the American forces — the United States surged into Iraq with the right commanders, additional forces and a fresh operational approach rooted in years of on-the-ground experience.