JUDY WOODRUFF:Earlier this week, we reported a new milestone crossed in the war in Afghanistan. The number of U.S. military deaths has surpassed 2,000.

Ray has the story behind the numbers.

GEORGE W. BUSH, former U.S. president:On my orders, the United States military has begun strikes against al-Qaida terrorist training camps and military installations of the Taliban regime in Afghanistan.

RAY SUAREZ:In 2001, President George W. Bush launched Operation Enduring Freedom. More than a decade later, the U.S. is still fighting in Afghanistan, and Americans are still dying.

While the numbers vary, the Department of Defense and others count at least 2,000 American military deaths since the war began. The number includes suicides in Afghanistan, but not those following service there. The death toll surpassed 1,000 back in 2010. That figure then doubled in just over two years after a major escalation.

PRESIDENT BARACKOBAMA:I have determined that it is in our vital national interest to send an additional 30,000 U.S. troops to Afghanistan, so that they can target the insurgency and secure key population centers.

RAY SUAREZ:What was called the surge sent more troops into dangerous Taliban territory.

Phillip Carter, a senior fellow with the Center for a New American Security, served nine years as an Army military police and civil affairs officer, including one year in Iraq.

PHILLIP CARTER, Center for a New American Security:It's a very infantry-centric war.

RAY SUAREZ:Carter says that jump in deaths is easy to understand when you look at the increase in the numbers, what the surge forces were asked to do and where.

PHILLIP CARTER:The fighting is concentrated in those places in Afghanistan that are most difficult to fight in, the plains of Helmand where we're really talking about canal-to-canal, or house-to-house fighting, the mountains of Eastern Afghanistan, where we see bloody combat reminiscent of Vietnam or, in some cases, even of Korea, very difficult to evacuate troops from if they're hurt, and that results in a high number of casualties for those troops committed to those areas.

RAY SUAREZ:The rising death toll also shed light on one military branch's role in the war.

PHILLIP CARTER:Most of these casualties in that second thousand occurred in the south, and that's where some of the most bloody fighting against the Taliban occurred. It's also where the Marine Corps put the majority of its effort, and I think that's why the Marines disproportionately suffered more dead than the Army or the Navy or the Air Force.

RAY SUAREZ:The website iCasualties.org lists two southern provinces, Helmand and Kandahar, as those with the most coalition fatalities during the war.

Department of Defense data also shows the majority of Americans killed were white men. Most were active-duty soldiers, as opposed to reservists, and between 25 and 30 years old. Still, the American death toll in Afghanistan is less than half that from the war in Iraq. The U.S. military effort there ended in December 2011.

PHILLIP CARTER:In Iraq, you had a much larger force go in and in a much more violent way initially than you had in Afghanistan. Then, that large force stayed for year after year after year, with 120,000, 150,000 troops on the ground.

Iraq was, for a long time, emphasized as the main effort, and Afghanistan was always seen as the supporting effort, and that drove the resourcing for that war.

It also, I think, drives the casualty numbers, that we're only now reaching a place in Afghanistan that we reached in Iraq many years ago.

RAY SUAREZ:Carter says the face of today's military force in Afghanistan is also much different, particularly when it comes to women, 36 of whom were killed in Afghanistan.

PHILLIP CARTER:Women have served our country extraordinarily well in Afghanistan, and they have served alongside with and in some cases died alongside with their male colleagues and brethren. When it comes to serving in combat, and serving in particularly arduous conditions where you can be killed, gender fades away, and it's all about whether you can do the job or whether you can't.

RAY SUAREZ:As the war in Afghanistan enters its 11th year, U.S. military forces have begun to draw down, with Afghan forces taking full control of security by the end of 2014.

But some fear those Americans on the ground today may be forgotten.

DEFENSE SECRETARY LEON PANETTA:Good afternoon.

RAY SUAREZ:Last week, Defense Secretary Leon Panetta called for the country's renewed attention.

LEON PANETTA:I thought it was important to remind the American people that there is a war going on in Afghanistan, and that young men and women are dying in order to try to protect this country.

RAY SUAREZ:The Afghan people are in the crossfire of those same battles, and Afghan security forces are seeing more deaths in their ranks. Civilian casualties have gone down this year compared to 2011, but remain high.

The United Nations reported just under 3,100 Afghan civilians were killed or wounded through June, 30 percent of them women and children.