The longest war: Scenes from two decades in Afghanistan

U.S. Army 10th Mountain Division soldier Jorge Avino from Miami, Florida carves the body count that their mortar team has chalked up on a rock, near the villages of Sherkhankheyl, Marzak and Bobelkiel, in Afghanistan, March 9, 2002.

U.S. Army soldiers from the 2nd Platoon, B battery 2-8 field artillery, fire a howitzer artillery piece at Seprwan Ghar forward fire base in Panjwai district, Kandahar province southern Afghanistan, June 12, 2011.

An Afghan man is detained by U.S. Marines from the First Battalion, Eighth Marines Bravo Company at their base in Talibjan after a battle against Taliban insurgents in Musa Qala district in southern Afghanistan's Helmand province November 7, 2010.

U.S. Army soldiers carry Sgt. Matt Krumwiede, who was wounded by an improvised explosive device (IED), towards a Blackhawk Medevac helicopter in southern Afghanistan June 12, 2012.

An Italian soldier from NATO cries as he carries a casket which contains the body of one of six Italian soldiers killed in Kabul, during a repatriation ceremony at the Kabul international airport, September 19, 2009.

U.S. troops from the Nato-led International Security Assistance Force (ISAF) light candles during Christmas Eve celebrations at Bagram Airfield, north of Kabul, December 24, 2014.

A group of men detained for suspected Taliban activities are held for questioning at a schoolhouse in the village of Kuhak in Arghandab District, north of Kandahar, July 9, 2010.

Soldiers from the U.S. Army's Alpha Battery, 425 Field Artillery, 3rd brigade of 10th Mountain Division based in Fort Drum, New York, fire their 155 mm Howitzer in Cop Cherokee base in Kherwar district in Logar province, October 4, 2009.

Sgt. William Olas Bee, a U.S. Marine from the 24th Marine Expeditionary Unit, has a close call after Taliban fighters opened fire near Garmsir in Helmand Province of Afghanistan, May 18, 2008.

Taliban fighters train with their weapons in an undisclosed location in Afghanistan, July 14, 2009.

A French sniper looks through his rifle's scope while keeping watch over Qarabagh district, north of Kabul, November 20, 2007.

A wounded Canadian soldier from the NATO-led coalition crawls for cover seconds after his position was hit by a Taliban shell fired from an 82-millimeter recoilless rifle during an ambush in Zhari district of Kandahar province, southern Afghanistan, October 23, 2007.

U.S. Marines fire during a Taliban ambush as they carry out an operation to clear an area in Helmand province, October 9, 2009.

Northern Alliance fighters ride on a T-62 tank past a dead body on the motorway north of Kabul, as Northern Alliance fighters approached the Afghan capital, November 13, 2001.

A French soldier of the 8th Artillery Regiment takes part in a joint patrol with U.S and Afghan troops in a village in Kharuti, in the mountains of Wardak Province in Afghanistan, July 16, 2009.