For the first time since 2001 there are no American troops in Afghanistan after the United States completed the evacuation of most of its citizens and thousands of at-risk Afghans.
More than 114,000 people have been airlifted from Kabul airport in the past two weeks after a speedy takeover by the Taliban.
But the end of the US military involvement in Afghanistan raises a new set of questions for Biden and his administration.
What happens to the people left behind who are at risk?
Tens of thousands of at-risk Afghans, such as interpreters who worked with the US military, journalists and women’s rights advocates, have been left behind. It is unclear what their fate will be but officials are concerned that the Taliban may retaliate against them.
The Taliban have pledged to allow all foreign nationals and Afghan citizens with travel authorisation from another country to leave Afghanistan, according to a joint statement issued by Ireland, Britain, the US and other countries on Sunday, but there are concerns about how they will be able to leave if there is no functioning airport.
The US evacuated more than 5,500 American citizens since evacuation flights began on August 14th. A small number have chosen to continue to stay in Afghanistan, many of them so they can be with family members.
What happens to Kabul airport after US forces leave?
For the past two weeks, the US military has been securing and operating Kabul's Hamid Karzai International Airport with nearly 6,000 troops.
The Taliban are in talks with governments such as Qatar and Turkey to seek assistance to continue civilian flight operations from there, the only way for many people to leave Afghanistan.
Turkish foreign minister Mevlut Cavusoglu said on Sunday that repairs need to be made at Kabul airport before it can be reopened to civilian flights.
Turkey, which is part of the Nato mission, has been responsible for security at the airport for the past six years. Keeping the airport open after foreign forces hand over control is vital not just for Afghanistan to stay connected to the world but also to maintain aid supplies and operations.
What does the future US-Taliban relationship look like?
The US has said it does not plan to leave diplomats behind in Afghanistan and will decide on what to do in the future based on the Taliban’s actions.
But the Biden administration will have to determine how it is able to ensure a humanitarian and economic crisis does not break out in the country.
The United Nations says more than 18 million people – more than half Afghanistan's population – require aid and half of all Afghan children under the age of five already suffer from acute malnutrition amid the second drought in four years.
Some countries including Britain have said that no nation should bilaterally recognise the Taliban as the government of Afghanistan.
What kind of threat is posed by Islamic State?
The one area of co-operation between the US and Taliban could be on the threat posed by Islamic State militants.
There are questions about how Washington and the Taliban can co-ordinate and potentially even share information to counter the group.
Islamic State Khorasan (ISIS-K), named after a historic term for the region, first appeared in eastern Afghanistan in late 2014 and quickly established a reputation for extreme brutality.
The group claimed responsibility for an August 26th suicide bombing outside the airport that killed 13 US troops and scores of Afghan civilians.
The US has carried out at least two drone strikes against the group since then and Biden has said his administration will continue to retaliate for the attack.
ISIS-K is a sworn enemy of the Taliban. But US intelligence officials believe the movement used the instability that led to the collapse of Afghanistan’s Western-backed government this month to strengthen its position and step up recruitment of disenfranchised Taliban members. – Reuters