Odierno and Petraeus came together last year to implement a newcounter-insurgency strategy that helped drive violence down,allowing Iraq to begin seeking foreign investment to rebuild afterdecades of war and UN sanctions.
Petraeus leaves behind a very different Iraq from the one he facedwhen he took over in February 2007, when Iraq was on the brink ofcivil war.
But Odierno is facing numerous challenges. On the security front,for example, he must ensure that Al Qaeda, already significantlyweakened, remains unable to incite sectarian bloodshed.
Iraq is expected to hold provincial elections at the end of thisyear or early in 2009. These will be followed by national polls inlate 2009.
Both elections could be a flash point for tensions between Arabsand Kurds with territorial disputes in the north, particularly inthe multiethnic city of Kirkuk, as well as rival Shiite factionsvying for dominance in the south, home to much of Iraq's oilreserves.
Iraq's Shiite-led government will also soon take control of SunniArab tribal units that joined forces with the U.S. military tofight Al Qaeda. Some analysts fear the tribal units, which includemany former Sunni Arab insurgents, could turn their guns on thegovernment if their demands are not met.
Starting next month, Petraeus will head U.S. Central Command, theheadquarters that oversees operations in the Middle East andbeyond, including the war in Afghanistan.
The Pentagon said it will pull 8,000 troops out of Iraq byFebruary, leaving 138,000 soldiers deployed there. The five extracombat brigades sent to Iraq last year completed their withdrawalin July and have not been replaced.
Despite the drop in overall violence in Iraq, the Bushadministration has taken a cautious approach to troop cuts, and anyfurther decisions on troop strength will be left to the next U.S.president after he takes office in January.
Officials and analysts say other factors played a big role inreducing violence in Iraq, including a decision by former SunniArab insurgents to turn against Al Qaeda as well as a cease-fireimposed by the Shiite cleric Moktada al-Sadr on his Mahdi army.