The US-led war in Afghanistan was a response to the September 11 terrorist attacks on America. Coalition forces toppled the ruling Taliban in 2001, but stabilising the country is proving more challenging.
Photo: An RAF crewman mans the machine gun mounted on the tailgate of his Chinook as it crosses the Afghan countryside in the morning mist, April 2002. (Getty Images)
On 11 September 2001 terrorists hijacked four aeroplanes in the United States. Two were deliberately flown into each of the Twin Towers of the World Trade Center in New York, with another hitting the Pentagon in Virginia. The fourth aeroplane crashed in a field in Pennsylvania.
The total loss of life on 9/11 was nearly 3,000. The 19 hijackers were members of al-Qaeda, the global Islamist network founded and led by Saudi-born Osama Bin Laden, now living in Afghanistan.
The US puts pressure on the Taliban
The Taliban, the ruling power in Afghanistan, were accused by the US of protecting Bin Laden. Taliban requests for negotiations with the US were rejected in favour of military action, and on 7 October 2001 the US-led Operation Enduring Freedom began in Afghanistan.
The aim of Operation Enduring Freedom was to find Osama Bin Laden, remove the Taliban from power, and prevent the use of Afghanistan as a terrorist haven. The US was supported by a broad coalition of international forces including the Afghan Northern Alliance, United Kingdom and Canada.
The Taliban fall from power
Kabul fell to coalition forces on 13 October 2001. In early December fierce fighting took place near the Tora Bora caves, where Taliban leader Mullah Omar and Osama Bin Laden were believed to be. Both men evaded capture and went into hiding.
Kandahar, the last major Taliban stronghold, fell on 7 December 2001, marking the end of the Taliban's rule in Afghanistan. They were excluded from the Bonn Agreement that formed a draft constitution for Afghanistan, and in 2004 Hamid Karzai was elected the country's president.
Beaten but unbowed, in 2002 the Taliban began a lengthy period of insurgency in an attempt to re-establish their power base. Meanwhile, international attention turned to Iraq, which US-led coalition forces invaded in 2003.
Control of operations switched to Nato's International Security Assistance Force (ISAF) in 2006. However, US troop numbers continued to grow throughout the decade in an attempt to contain the Taliban.
A new wave of terror
The Taliban insurgency involved increasing use of roadside bombs and suicide attacks. The numbers of Nato troops in Afghanistan grew, but this brought little success. "The Taliban fighters reservoir is practically limitless," the UN's Tom Koenigs told the German newspaper Der Spiegel in 2006. "The movement will not be overcome by high casualty figures."
Although there had initially been broad public support for the war in Afghanistan in the US and UK, polls suggested a falling in confidence as costs spiralled and casualty numbers rose. What had started as an operation to remove the Taliban and al-Qaeda had become an expensive damage limitation and state-building exercise.
On 20 November 2010, Nato announced the withdrawal of international forces from Afghanistan by 2014. The plan, signed by Hamid Karzai and the UN's secretary general Ban Ki-moon, would see control handed to the new Afghan army (ANA) and police force.
Nato countries agree to troop withdrawal
In June 2011 US President Barack Obama announced that 10,000 US troops would leave Afghanistan by the end of the year, and an additional 23,000 would leave by 2012. Canada withdrew all its troops in 2011, and other Nato countries pledged to reduce their military presence.
In the UK, prime minster David Cameron pledged to end British combat operations in Afghanistan by 2015. "I believe the country needs to know there is an end point to all of this," he said, "so from 2015 there will not be troops in anything like the numbers now and crucially, they will not be in a combat role."
In a covert operation, US Navy SEALs (a special operations force) and CIA operatives killed Osama Bin Laden on 2 May 2011, in his residential compound in Abottabad, Pakistan.
Al-Qaeda swore to avenge Bin Laden's death. A statement posted on jihadist websites stated: "We will remain, God willing, a curse chasing the Americans and their agents, following them outside and inside their countries."