Gen. David Petraeus, who oversaw a reversal in rising violence in Iraq, turned over control of U.S. forces in the country to Gen. Ray Odierno on Tuesday.
Petraeus took over in February 2007, a month in which six U.S. helicopters were shot down, deadly bombings were common and nearly 500 bodies turned up in the capital, reported CNN.
Since then, the "surge" has become a buzzword in American politics. The temporary influx of 31,000 U.S. troops is credited, in part, with reducing violence across Iraq.
"I think that Gen. Petraeus will be regarded by history, by military historians, as a great American military strategist," said Martin Navias, defense analyst for the Center of Strategic Studies at Kings College in London. "When he came into power ... the situation in Iraq was terrible. He supported a surge."
Sectarian violence is down, according to the U.S. military, from 60 incidents a week to what it now calls "negligible levels."
U.S. troop deaths are down as well.
In 2007, 906 American troops died in Iraq, the deadliest year of the war. Through Monday, nearly nine months into the year, the U.S. death toll was 248.
Petraeus says the future of Iraq is still uncertain.
"There are many of these possible storm clouds that are out there," he told CNN. "So Ray Odierno and the CENTCOM future command will still have lots of rocks in our rucksack."
CENTCOM is the U.S. Central Command, the military command responsible for a region of the world that includes Iraq. Petraeus' next assignment is commander of Central Command
Refugees, internal Iraqi politics and the restoration of basic civil services are just a few of the issues Odierno will have to deal with as the commander of U.S. forces in Iraq.
Odierno's strategy is expected to pick up where Petraeus' left off.
U.S. troops have spread out across the country, tracking insurgents as they've fled the population centers.
The U.S. military is working with former Sunni insurgents in groups known as "awakening councils." The groups are getting much of the credit for keeping violence down.
Odierno is known for not being afraid to show emotion in front of his troops. His son, as a captain in the Army, lost his arm in battle in Iraq in 2004.