- War in Afghanistan (2001-present)
Over 800,000 US military members served in Afghanistan during America's longest war. Over 2,000 were killed and more than 20,000 were injured.
The United States spent $822bn (£598bn) fighting the war and training Afghan forces, only to witness the Taliban's rapid conquest of the country.
Four veterans who served in Afghanistan reflect on the war and the fall of the country they tried to help rebuild.
Jason served in the US Army and was deployed to Kandahar, Afghanistan in 2010.
I feel like I'm watching the end of the movie Titanic. You knew the ship was going to sink, you just didn't know when or how quickly.
I think what Biden said about the Afghan forces being unwilling to fight was harsh, but true. It's not surprising the Afghan army fell quickly. They couldn't hold rural areas once we ended the surge a decade ago. The cities were next, with the smaller ones falling first. Afghan soldiers were not going to keep dying for what looked inevitable. I don't blame them. The only partially surprising part is the Taliban didn't wait until we were completely out of the country to take the capital.
The US should not have stayed – this was always going to happen. When Biden said staying in Afghanistan for one or five more years wouldn't have changed things, he's absolutely correct.
Serving in the war made me re-evaluate how I feel about war in general – you realise how much of it is out of your control. So much of what the US wanted to accomplish there was contingent on what others needed to do, like Pakistan, Afghan soldiers, local citizens. Nobody was on the same page in Afghanistan.
It's unfathomable that people let it go on for so long.
Michelle is a member of the US Air Force and was deployed in 2016.
I'm disappointed in our behaviour as a country. It's very sad. I feel so badly for all the Afghans. Especially the females who will now be put back in the dark ages under the Taliban.
Look at Vietnam. Look at Korea. War is never worth the cost. Was this one done correctly? Apparently not. The Taliban went into hiding and waited everyone out.
Did we do a full assessment of the capabilities of the Afghan army? I don't think so. We trained helicopter pilots. We allegedly trained their soldiers. But apparently we didn't do a very good job.
- How much has the Afghanistan war cost?
I think the exit should have been different. After 20 years, that's a whole generation of people. There are young Afghans I met there who looked up to the American military. They wanted to work with Americans. There was a good living and a standard of life. Now it's gone.
Can we change it? No. Is this a Democrat versus Republican issue? No… nobody had a plan. I am just truly disappointed.
Mike Jason is a retired US Army colonel who served for 24 years.
It's frustrating. It's maddening. The speed at which this started collapsing makes it very hard. It's faster than our ability to process our experiences over the last 20 years.
I've been texting with an Afghan senior officer in hiding right now. His family is in hiding. There's a real life crisis going on. For veterans, this isn't about us right now. Our friends are in real danger today. It's not over yet. This is not the time to feel sorry for ourselves.
I am an idealist who joined the Army because I wanted to do good. When 9/11 happened, I wanted to do something. When we got to Afghanistan, it was a lesson in empathy, working in foreign cultures, seeing a beautiful country with a rich history.
Was it worth it? Was my role worth it? At the time I thought I'd done some good – but now I need time to reflect.
We created a military for a country that did not yet exist, a colleague of mine once said. The Afghan army felt no loyalty to a government that they saw as corrupt and illegitimate. I don't know if more US troops would have stopped the inevitable.
I don't know that anybody who worked on the ground there is particularly shocked at the outcome.
The tragedy is that there are people in Afghanistan that just want their kids to grow up and be safe. For some, they had a taste of what that's like when we were there, and now darkness has returned.
Kyle Hanson served in the US Army from 2006 to 2012.
I'm feeling a lot of different emotions. I feel sadness for so much of my fellow comrades' youth spent and lost for this cause. However, I certainly do not feel shock – it has long been known the ineffectiveness of the Afghan state and military.
This was known to be what would happen when we left. American politicians passed it back and forth for 20 years, but the war stopped being worth it shortly after it began.
I'm not surprised by how quickly the Afghan army fell – the Taliban had been given plenty of time to prepare, and given nearly exact dates to work with.
Should we have stayed? I don't think staying was an option, but the way the pull out was handled by the Trump and Biden administrations was callously dictated by US domestic politics. There was also a lack of honesty of the situation on the ground in Afghanistan to the American people.
War is an extension of politics. Our military tried its best, and our politicians let us and the Afghans down.