Currently 8,400 American soldiers are taking part in NATO's operation in Afghanistan, which comprises a total of 13,000 troops in all. Most of them are charged with overseeing and training Afghan forces.
War on terror
On October 7, 2001, less than a month after the September 11 attacks, US president George W. Bush launches operation "Enduring Freedom" in Afghanistan, after the Taliban regime refuses to hand over Al-Qaeda chief Osama bin Laden.
In a matter of weeks the US-led forces overthrow the Taliban, in power since 1996.
Apart from air strikes, the US backs the Afghan Northern Alliance, which is fighting the Taliban, contributing paramilitary teams from the CIA and special forces.
Some 1,000 American soldiers are deployed on the ground in November, rising to 10,000 the year after.
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Forgotten war
Attention is diverted from Afghanistan as US forces in 2003 mount an invasion of Iraq, which becomes the main US concern.
The Taliban and other Islamist groups regroup in their strongholds in the south and east of Afghanistan, from where they can easily travel to and from Pakistani tribal zones.
In 2008 the American command on the ground calls for manpower to carry out an effective strategy against the Taliban insurgency. Bush agrees to send additional soldiers and by mid-2008 there are 48,500 US troops there.
Peak of 100,000 troops
In 2009, in the first months of the presidency of Barack Obama -- elected on campaign promises to end the two wars in Iraq and Afghanistan -- there is a surge in the number of American soldiers in Afghanistan to around 68,000.
In December, Obama raises the strength of US forces in Afghanistan to around 100,000.The objective is to put brakes on the Taliban and to strengthen Afghan institutions.
Death of Bin Laden
Al-Qaeda leader Bin Laden, mastermind of the 9/11 attacks that started the war, is killed on May 2, 2011 during an operation by US special forces in Pakistan, where he is in hiding.
End of combat operations
In September 2014 Afghanistan signs a bilateral security accord with the US and a similar text with NATO: 12,500 foreign soldiers, of which 9,800 are Americans, will remain in the country in 2015, after the end of the NATO combat mission at the end of 2014.
From the beginning of 2015, American troops will be charged with two missions: anti-terrorist operations against Al-Qaeda and the training of Afghan forces.
In late December, the NATO combat mission ends, and is replaced by an assistance mission baptized "Resolute Support".
However, the security situation degenerates.
Amid a resurgent Taliban, on July 6, 2016, Obama again slows down the pace of withdrawal, saying that 8,400 US troops will remain in Afghanistan into 2017.
MSF clinic bombed
On October 3, 2015, at the height of combat between Islamist insurgents and the Afghan army, backed by NATO special forces, a US airstrike bombs a hospital run by Medecins Sans Frontiers (Doctors Without Borders) in northern Kunduz province, killing 42, including 24 patients and 14 members of the NGO.
Mega bomb against IS
On April 13, 2017, the US military drops the largest non-nuclear bomb it has ever used in combat, hitting Islamic State positions in a network of tunnels and caves in the east, killing 96 jihadists.
In July, the American army kills the IS's new leader in Afghanistan, the third such chief slain by Washington and Kabul.
New strategy
On February 1, 2017 a US government report says that losses of Afghan security forces have climbed by 35 percent in 2016 compared with the previous year.
On February 9, the US general in command of the NATO force, General John Nicholson, warns that he needs thousands more troops, telling Congress: "I believe we're in a stalemate."
On August 21 Trump cleared the way for the deployment of thousands more US troops to Afghanistan in his first formal address to the nation as commander-in-chief.
Following the president's speech Monday US Defense Secretary James Mattis announced Monday that America and several allies have committed to boosting their troop numbers in Afghanistan.
Senior White House officials say President Donald Trump has already authorized Mattis to deploy up to 3,900 more troops to Afghanistan.
