BAGHDAD -- The second half of 2007 saw violence drop dramatically in Iraq, but the progress came at a high price: The year was the deadliest for the U.S. military since the 2003 invasion, with 899 troops killed.
American commanders and diplomats, however, say the battlefield gains against insurgents such as al-Qaida in Iraq offer only a partial picture of where the country stands as the war moves toward its five-year mark in March.
Two critical shifts that boosted U.S.-led forces in 2007 -- a self-imposed cease-fire by a main Shiite militia and a grassroots Sunni revolt against extremists -- could still unravel unless serious unity efforts are made by the Iraqi government.
Iran also remains a major wild card. U.S. officials believe the neighboring country has helped quiet Iraq by reducing its flow of suspected aid to Shiite fighters, including materials needed for deadly roadside bombs.
But Iran's apparent hands-off policies could come under strain as Shiite factions -- some favoring Iran, others not -- battle for control of Iraq's oil-rich south.
The Pentagon, meanwhile, will increasingly look to the uneven Iraqi security forces to carry the load in 2008 as demands for an American exit strategy grow sharper during the U.S. election year.
Britain, the main U.S. coalition partner in Iraq, is gradually drawing down its forces and other allies, including Poland and Australia, are contemplating full-scale withdrawals in the coming year.
"We're focusing our energy on building on what coalition and Iraqi troopers have accomplished in 2007," Gen. David Petraeus told a group of Western journalists Saturday. "Success will not, however, be akin to flipping on a light switch. It will emerge slowly and fitfully, with reverses as well as advances, accumulating fewer bad days and gradually more good days."
That arc of progress played out in the raw statistics of U.S. and Iraqi casualties.
American military deaths peaked in May with 126 troops killed. It was then that the U.S. began ramping up its attacks against insurgent strongholds, leading to increased clashes in Baghdad and other key areas across central Iraq.
Seven months on, commanders and analysts say America's aggressive strategy of targeting al-Qaida in Iraq strongholds is paying off: U.S. casualties have dropped sharply. As of Sunday night in Baghdad, 21 deaths were reported in December, the second lowest monthly total of the war.
The 899 deaths in 2007 surpassed the previously highest death toll in 2004, when 850 U.S. soldiers were killed. The total for 2007 could rise slightly; occasionally the military reports new casualties a few days after they occur. The military reported the noncombat related death of a soldier Sunday.
Since the influx of some 30,000 U.S. troops that began in June, the lessening violence has meant that new problems have emerged.
"There certainly are ample challenges out there in the new year. In some respects, the positive developments in the latter half of 2007 also represent the challenges of 2008," U.S. ambassador Ryan Crocker said during a recent briefing.
An example, Crocker said, is how the improving security situation is in part luring back Iraqis who took refugee in neighboring Syria, Jordan and elsewhere.
"The return of refugees -- a good thing obviously, but a process is going to have to be carefully managed so that it doesn't sow the seeds of new tension and instability," he said.