Timeline: US intervention in Afghanistan

a group of people in uniform: The US formally begins withdrawing its troops from Afghanistan on Saturday © Wakil KOHSAR The US formally begins withdrawing its troops from Afghanistan on Saturday

The US-led invasion of Afghanistan in 2001, following the 9/11 terror attacks, targeted Al-Qaeda in the sanctuaries provided by the then Taliban government.

As the US formally begins withdrawing its troops from the country Saturday, bringing its longest war nearer to an end, a timeline of the last two decades:

- 'War on terror' -

On October 7, 2001 -- less than a month after the September 11 attacks that killed around 3,000 people in the US -- President George W. Bush launches operation "Enduring Freedom" in Afghanistan.

The country's Islamic fundamentalist Taliban regime had been sheltering Osama bin Laden and his Al-Qaeda movement, which carried out the attacks.

The operation opens a military front in the US "war on terrorism".

Within weeks, US-led forces overthrow the Taliban, in power since 1996.

About 1,000 American soldiers are on the ground by November 2001, rising to 10,000 the next year.

- Forgotten war -

American attention is diverted from Afghanistan when US forces invade Iraq in 2003 to oust dictator Saddam Hussein.

The Taliban and other Islamist outfits regroup in their strongholds in southern and eastern Afghanistan, from where they can easily travel between their bases in Pakistan's tribal areas, and launch an insurgency.

In 2008, the US command in Afghanistan calls for more manpower. Bush sends additional soldiers and about 48,500 US troops are deployed.

- Peak of 100,000 troops -

In 2009, Barack Obama -- elected president on campaign promises to end the Iraq and Afghanistan wars -- boosts the US deployment to around 68,000. In December, he sends another 30,000. 

Video: US officials confirm beginning of Afghanistan troop withdrawal (ABC News)

Timeline: US intervention in Afghanistan