Now, as the challenges change from military, to economic and political, a new man is taking over - he is General Ray Odierno, known as "General O."
This is his third tour of duty in Iraq. In 2003 he led the 4th Infantry Division that captured Saddam Hussein. In 2007, he became Gen. Petraeus' number two. And now, after seven months in the States, he's back and in command.
Gen. Ray Odierno is 54, a West Point graduate and former artillery officer. In a ceremony at one of Saddam Hussein's former palaces - now the U.S. military headquarters in Iraq - he took command from Gen. Petraeus, whose big shadow he must now come out from under.
So on day two as commander, he began a tour to establish his authority and make his first battlefield assessment, flying south to the so-called "Triangle of Death."
"Would you go so far as to say this was one of the absolute worst parts of Iraq in terms of violence?" correspondent Lesley Stahl asked.
"Yeah, it absolutely was one of the very worst parts of Iraq in violence," Odierno replied.
The general surveyed a quiet neighborhood in the Triangle of Death. The area, just south of Baghdad, was tamed with the help of former Sunni insurgents who the Americans paid to change sides and turn their guns against al Qaeda in Iraq.
"This was where al Qaeda staged a lot of its raids and rockets and IEDs. What happened to them? Where have they gone?" Stahl asked.
"Well, I mean, first off, we've eliminated a lot of them," Odierno replied.
"Killed 'em," Stahl remarked.
"Well, we've captured 'em, killed 'em," Odierno said, walking with Stahl. "And really what's happened is their passive support base, that they got from the population, is gone."
Odierno said he hadn't walked down this neighborhood street in a long time.
"I mean, this is amazing," he told Stahl.
He should feel good: he was the one who devised the battle plan for the Triangle of Death. Now there are Iraqi army troops and Sunni civilian patrols everywhere. A year ago, there were about 100 attacks a week there. Now, there are only two.
"You have about 30,000 people now that help with security, where back a year ago you probably had maybe a thousand," Odierno told Stahl.
"So a thousand to 30,000. Well, no wonder it's calmed down," she remarked.
Al Qaeda in Iraq used to extort protection money from the local shop owners. Now that that has stopped, too, the local market is flourishing for the first time in years.
"We now have people starting their own businesses. They're now able to earn a living, an honorable living for their family. They're not afraid to come out. I would say 75 percent of the country, maybe even more, is more like this," Odierno told Stahl.
In Baghdad, for instance, where car bombs and corpses in the streets had become a way of life, you see things the Iraqis thought they'd never see again: laughter in the markets that are crowded and thriving. Nightlife has returned, and people who used to live in fear, take their children to the zoo.