David Petraeus, the retired four-star Army general, served in the military for nearly four decades, eventually becoming the most famous and revered member of the armed forces during the war on terror and the war in Iraq. Known for developing a new theory of counter-insurgency, which emphasized winning the support of civilians rather than seizing territory, Petraeus was placed in charge of all troops in Iraq by President George W. Bush in 2007 and oversaw the so-called surge of forces meant to turn around a faltering war effort. In 2010, President Barack Obama, who had ordered a surge of troops in Afghanistan—a move opposed by then Vice-President Joe Biden—appointed General Petraeus the commander of forces in that country. Petraeus retired from the military the following year, and went on to serve as Obama’s C.I.A. director. He resigned from that post in 2012, after providing classified information to his biographer, Paula Broadwell, with whom he was having an affair. Petraeus later pleaded guilty to one count of mishandling classified information. He is now a partner in the global investment firm K.K.R. and chairman of the K.K.R. Global Institute.

On Wednesday, Petraeus and I talked by phone about the situation in Afghanistan. We spoke for nearly eighty minutes; Petraeus was passionate about how he felt the Biden Administration had erred in the withdrawal, and why he thought it was wrong to blame Afghan forces for the collapse of the government. He believes the U.S. should have remained in Afghanistan, and gave a full-throated defense of an active military presence abroad. Our conversation, edited for length and clarity, is below.

How do you think the situation in Afghanistan ended up where it is today?

It started with the Trump Administration, and not getting much of an agreement [with the Taliban], to put it mildly. We forced the Afghan government, which was not allowed to be in the negotiations about the future of their country, to release more than five thousand Taliban fighters, and didn’t get anything significant in return. And of course the new Administration came in and did a quick review and analysis and announced the decision to withdraw, which you may recall that at the time I said I feared we would come to regret. And I think we already have. That was a psychological blow, I think, the significance of which may not have been obvious to all.

Then you actually had the withdrawal. And this was not of forces in frontline combat. What we had were advise-and-assist units, who were located in the headquarters of the Afghan forces, and they include essentially liaison teams and tactical air controllers who can—with the aid of drones over the top of battlefields—confirm the targeting necessary for true close air support. We are not talking about bombing the mountain over there. We are talking about bombing as close to troops in combat as was possible. And that was quite an elaborate structure, and it was enormously important to the Afghans, who still had a very modest-sized air force. But if you don’t have the liaison teams with the Afghan headquarters who are sitting next to an Afghan commander who is getting radio reports from his people and often looking at the same feed of what a Reaper drone is seeing underneath it, it is really hard to bring serious airpower to bear.

So you have the withdrawal of U.S. forces, which includes not just the airpower but the systems and people who enable its use in close air support. And, somewhat overlooked, although some of us did identify this months ago, the departure of some eighteen thousand contractors who maintain the U.S.-provided Afghan air force and also manage the maintenance system. It is a huge system that involves supply chains and regular inspections—a lot of very sophisticated diagnostic equipment, tools, and this enormous logistic support structure to provide these spare parts in a very austere environment. And of course they are also being shot up by the Taliban.

That air force worked very, very hard. And they are trying to ferry commandos who are really quite good fighters, very well trained by our Special Ops, and well equipped. And they did go out in these early battles, and they were holding off the Taliban, but I think at a certain point in time they realized that there was nobody coming to the rescue anymore, nobody has our back, there is no emergency resupply, there are no reinforcements, there is no emergency medical evacuation, and there is no close air support. And I think that happened in a couple of cases, and those troops did what I think troops do in those circumstances, if they are left alone and isolated and no one is coming to the rescue. Along with local leaders of those districts or provinces, they either cut a deal or they negotiate a surrender or they flee. And then I think the psychological collapse of the Afghan military set in. And I think that was infectious. You talk about infectious enthusiasm. This was an epidemic of, basically, surrender.

Was there an error somewhere along the way, given that when we pulled out this collapse just happened? How did we not prepare for that in twenty years?

I just think it was premature to leave. Now, you can say, Well, when do you leave? Ideally you say that there are certain conditions. Let’s keep in mind that everyone is criticizing nation-building. Well, part of nation-building is developing security forces. It is developing institutions that can take over tasks that we were provided. Undoubtedly, there were innumerable mistakes made in the name of nation-building and infrastructure overbuilt. You can name the different shortcomings. But, again, you have to build something you can hand off. Keep in mind that, once we topple the Taliban, we own the country. It’s easy to say, “You got Osama Bin Laden. What are you hanging around for?” Well, because Al Qaeda will be back. If there is one thing we should have learned in the last twenty years of war, it’s that if you don’t keep an eye on an Islamist extremist group, it will come back.

You think that’s the main lesson?

Well, there are a lot of lessons. There are actually five lessons from the last twenty years of war, if you want to hear them.

Yes, please.

The first is that Islamist extremists will exploit ungoverned spaces, or spaces governed by kindred spirits in the Muslim world. It is not a question of if, it is a question of when and how it will be.

Sorry, General, there is some wind.

I was walking. The sign I am really serious about this, and giving someone my best attention, is that you walk the dog instead of doing it in front of a screen. Lesson No. 2 is that you actually have to do something about this problem itself. You can’t study it until it goes away. We did that for a time with respect to the Islamic State in Syria, and it wasn’t until they had generated enormous combat power, swept back into Iraq, established the caliphate in northern Iraq and northeastern Syria, carried out activities on social media to galvanize and instigate terrorist attacks. You have to do something, because what happens there doesn’t stay there. It’s not Las Vegas rules. It’s the opposite. And these situations tend to have violence, extremism, instability, and, most significantly in the case of Syria, a tsunami of refugees in our NATO allies, causing the biggest domestic political challenges since the end of the Cold War.

No. 3, in doing something, the U.S. generally has to lead, and that is because we have such an enormous preponderance of military capabilities—in particular when it comes to the assets that are the most useful in the way we have been able to fight in recent years, which is by advising, assisting, and enabling host nations’ forces with the armada of drones we now have, and an unequal ability to fuse intelligence. Now, that doesn’t mean that we shouldn’t have a coalition. We should. And let’s remember we did in Afghanistan. And you should have Muslim partners with you, as we did. By the way, the validation of No. 3, that the U.S. had to lead, is that, when the United States departed Afghanistan, the coalition countries all departed as well, even though many if not most wanted to stay. We know the U.K. wanted to stay. You saw people in the U.K. Parliament say, “We can’t do anything independently?” The answer unfortunately is probably not.

You are giving rules and saying why they are important, but, when someone asks why the things you say were necessary didn’t happen in Afghanistan in twenty years, how do you understand the answer?