JUDY WOODRUFF: Now, the war in Iraq and the loss of 4,000 Americans. Ray Suarez has this overview report on the American toll so far.
RAY SUAREZ: There's been a rise in violence in Iraq, lethal for Americans and Iraqis. But it's also true that for months now, starting late last year, American casualties have been dropping, the first sustained drop since the war began five years ago.
Until the fall, roughly 80 to 100 troops were killed in each month of 2007. But in September, eight months after tens of thousands of additional troops began arriving as part of the surge, the death toll began dropping to 40 or fewer a month.
Last month was one of the least deadly for American troops since 2004: 29 Americans were killed in Iraq in February.
Chuck Vinch tracks casualty information for the Military Times News Service.
CHUCK VINCH, Military Times News Service: Around the middle of the summer, we saw something change there and the numbers started to drop. That was about the point where the surge was completed, the surge of the five additional combat brigades into Iraq was completed, and they were pretty much all in place and doing what they were supposed to be doing. And around August, we started to see a bit of a slowdown, September, and then into the fall it really became noticeable.
RAY SUAREZ: Since the U.S. invaded Iraq, more than 4 out of every 5 deaths came in hostilities. The number-one threat is what it's been for years: the IED, or improvised explosive device, responsible for more than 50 percent of all U.S. deaths so far.
More than 21 percent of the dead were killed in other hostile fire. Among non-hostile deaths, vehicle or helicopter accidents have been the most deadly, responsible for 8 percent of American fatalities.
Baghdad and other provinces at the center of the country are the deadliest locations now. More than 1,200 Americans have been killed in and around Baghdad so far.
The western Anbar province has been even deadlier throughout the course of the war and the insurgency; nearly 1,300 have died there. But the surge and Sunni cooperation with U.S. forces has brought less fighting and fewer casualties to that region in recent months.
Of all branches of the military, the Army, with the most members in Iraq, has suffered the heaviest losses. More than 70 percent of the dead were members of the Army, including reservists and Army National Guard.
The smaller Marine Corps accounts for nearly a quarter of all deaths, nearly 1,000 to date. The Marine casualty rate has fallen in recent months.
CHUCK VINCH: Marine casualties have dropped significantly, and it's mainly because the Marines' main responsibility has been Anbar province. So, as the violence in Anbar province has declined, so, too, has the rate of casualties among U.S. Marines.RAY SUAREZ: The remaining 5 percent of casualties come from the Navy and Air Force. The Navy has lost more than 90 personnel, the Air Force about 45. Eighty-three percent of all deaths were among active-duty personnel; 10 percent of the deaths were from the National Guard; 6 percent were reservists.