REUTERS/Jason Reed
Then-US Secretary of Defense Robert Gates, left, and US Army Gen. David McKiernan, top US and NATO commander in Afghanistan, with Afghan officials in the mountains of Wardak Province, May 8, 2009.
At the end of 2014, after more than 13 years of combat operations, 9,800 US troops were to remain in Afghanistan.
That number would be reduced by half at the end of 2015 and reduced again at the end of 2016 to a small military contingent attached to the US embassy.
But the Taliban's continued success on the battlefield and Afghan security forces' poor performance led to a continued US deployment in the country.
At the end of 2016 the US had a force of nearly 10,000 in Afghanistan, though President Barack Obama intended to reduce that force to 5,500 in 2017, the Taliban threat caused a change of plans, and 8,400 troops are to remain in Afghanistan during 2017.
Now the Trump administration is considering sending up to 5,000 more troops to to support Afghan military and police units fighting the Taliban, as well as deploying special-operations forces to counter ISIS and Al Qaeda elements along the Afghan-Pakistan border.
Those deliberations come as the US is failing in its nearly 16-year-long fight - longer than any other US foreign war and most other military operations - in the war-torn country, according to Defense Secretary James Mattis.
"We are not winning in Afghanistan right now. And we will correct this as soon as possible," Mattis told the Senate Armed Services Committee on Tuesday.
Mattis is not alone in that assessment.
REUTERS/James Mackenzie
US Army Gen. John Nicholson, commander of US forces in Afghanistan, with US soldiers during a transfer of authority ceremony in Helmand province, April 29, 2017.
Earlier this year, Army Gen. John Nicholson, the top US commander in Afghanistan and the 12th person to hold that job, called the situation there a stalemate.
Nicholson has also cautioned Congress that more US forces may be needed to counter growing outside influence in Afghanistan - from Russia in particular.
In 16 years of operations in and around Afghanistan, the US has lost some 2,200 troops.
Since 2001, the US has spent about $110 billion on Afghanistan's reconstruction, more than the cost of the Marshall Plan that reconstruct Europe after World War II. Washington has allocated more than $60 billion since 2002 to train and equip Afghan troops.
The US money spent in Afghanistan has yielded few lasting results, however. Security in the country remains precarious and the Taliban is believed to control more territory in Afghanistan than at any time since 2001.
Below, you can see photos documenting the last 16 years the US's "generational" war in Afghanistan.