The longest war: Scenes from two decades in Afghanistan

A rocket fired by U.S. soldiers from Dragon Troop of the 3rd Cavalry Regiment explodes next to a destroyed bus at operating base Gamberi in the Laghman province of Afghanistan December 31, 2014. (Image: Reuters)

A U.S. soldier from the 3rd Cavalry Regiment pays his respects during a memorial for Specialist Wyatt Martin and Sergeant First Class Ramon Morris at Bagram Air Field in the Parwan province of Afghanistan December 23, 2014. Specialist Martin and Sergeant First Class Ramon were killed on December 12th by an improvised explosive device while on patrol near Bagram Air Field. (Image: Reuters)

Smoke and flames rise from fuel trucks after an overnight attack by the Taliban on the outskirts of Kabul July 5, 2014. Taliban insurgents set fire to about 200 oil tanker trucks supplying fuel for NATO forces in an attack just outside the Afghan capital Kabul, police said. (Image: Reuters)

U.S soldiers blow up a roadside bomb set up by Taliban fighters near the town of Walli Was in Paktika province, near the border with Pakistan, November 4, 2012. (Image: Reuters)

U.S. and Afghan soldiers walk near a U.S. Army Chinook during an operation near the town of Walli Was in Paktika province November 1, 2012. (Image: Reuters)

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. (Image: Reuters)

Two 500 pound bombs explode at dusk on a Taliban fighting position near Blocking Position one above Kamdesh in Afghanistan's Nuristan Province June 11, 2012. (Image: Reuters)

Jake Beaudoin, a U.S. Army Private of 508 BSTB, 4th Brigade Combat Team, 82nd Airborne Division, takes cover during a controlled detonation to clear an area for setting up a check point in Zahri district of Kandahar province, southern Afghanistan May 31, 2012. (Image: Reuters)

Members of the U.S. Navy carry a comrade wounded by an explosion to a medevac helicopter in Kandahar province in southern Afghanistan October 2, 2010. (Image: Reuters)

Captain Melvin Cabebe with the US Army's 1-320 Field Artillery Regiment, 101st Airborne Division stands near a burning M-ATV armored vehicle after it struck an improvised explosive device (IED) near Combat Outpost Nolen in the Arghandab Valley north of Kandahar July 23, 2010. (Image: Reuters)

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. (Image: Reuters)

A U.S. soldier of 2-12 Infantry 4BCT-4ID Task Force Mountain Warrior takes a break during a night mission near Honaker Miracle camp at the Pesh valley of Kunar Province August 12, 2009. (Image: Reuters)

British soldiers from B Company, 2 Mercian, set off on an operation in Malgir, Helmand province July 27, 2009. (Image: Reuters)

A French army 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. (Image: Reuters)

An Afghan boy looks at a German armed forces Bundeswehr soldier during a patrol in a village in Kunduz province, April 26, 2009. (Image: Reuters)

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. (Image: Reuters)

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. One Canadian soldier was lightly wounded and an Afghan National Army soldier was shot in the shoulder during heavy fighting in the volatile Mowz-e-Madad area of Kandahar province. (Image: Reuters)

United States Army 10th Mountain Division soldier Jorge Avino from Miami, Florida carves the body count that their mortar team has chalked up on a rock, March 9, 2002 near the villages of Sherkhankheyl, Marzak and Bobelkiel, in Afghanistan. The team said they have killed 40 plus people, hit 12 vehicles and destroyed 1 mortar team near the villages were an al Qaeda and Taliban stronghold came under intense bombing and firefights as the coalition forces battled to root them out. (Image: Reuters)

U.S. Marines begin to form up their convoy at a staging area near Kandahar, Afghanistan, as they await orders to begin their trek to Kandahar to take control of the airfield on December 13, 2001. (Image: Reuters)

A US Marine Humvee kicks up dust as it crosses a group of Marine LAVs (Light Armoured Vehicles) as it leaves on patrol from the Marine base in southern Afghanistan December 2, 2001. The Marines of the 15th MEU (Marine Expeditionary Unit) arrived in southern Afghanistan November 25 night and took command of a secret airstrip, establishing a significant military presence in Afghanistan. (Image: Reuters)