Saturday marks the 20th anniversary of the Sept. 11, 2001 attacks that took 2,977 lives and changed the world forever. It permanently altered the security landscape in the United States and elsewhere, forcing governments to completely overhaul their defense strategies, policies and counterterrorism tactics. 

Twenty years on, events in the very country that harbored the perpetrators of the 9/11 attacks — Afghanistan — have seen the War on Terror come something like full circle.

The collapse of Afghanistan following the U.S. troop withdrawal, and its takeover by the Taliban — the group that hosted al-Qaeda as it plotted its attacks on the West — for many represents a symbolic and devastating failure.  

In the last two decades of the war against terrorism, millions of lives have been lost and trillions of dollars spent. CNBC spoke to CIA, military and diplomatic veterans of the ongoing War on Terror, asking what they feel America has learned — and failed to learn — since Sept. 11, 2001.

Nada Bakos, former CIA analyst

“Honestly, I don’t think we’ve learned that much; I think we’re probably destined to be making some of those mistakes again. But hopefully we’re done with giant occupations of other countries. 

“I hope that we have gotten to the point now where we understand that we can’t spread our democracy and rebuild other countries in our model, in a way that we were naive enough to think would work at that time.”

Jim, former U.S. Marine and Afghanistan war veteran 

“We’ve learned that 20 years of war has made us the best in the world at small unit tactics, but continuing to fight insurgencies is none of our business.  

“I think many Americans have learned not to trust their government. ‘Leadership’ lied to the American public for 20 years, while the actual situation on the ground in Afghanistan was no mystery to the people who served there. This has gone on for two decades as senior ‘leadership’ moves from the military or government into high-paying defense contractor jobs. 

“Here’s the scary thing though: I don’t think the general public has learned anything. They haven’t been invested in the GWOT [Global War on Terrorism] on a large scale. If they had been, they would be demanding accountability for the entire thing, with the debacle in Kabul as the catalyst.” 

Jim requested his last name be withheld due to professional restrictions on speaking to the press. 

William Patey, former U.K. ambassador to Afghanistan and Iraq

“We certainly learned the limitations on the use of force in dealing with a problem such as global terrorism — we’ve learned it’s more complicated, and that liberal democracies are not very good at devoting the necessary time and resources to doing the work. They are impatient, and their political horizons are very short.

“What we’ve also learned since 9/11 is that the radical Islamist threat remains as potent as ever, it hasn’t gone away. And importantly, we’ve learned that radical Islamist ideology is not Islam. It’s different.

“We continue to have things like war on terrorism, war on drugs. These are wars that fail. These are ongoing societal and ideological questions that need complex, difficult policies that are not easily dealt with by something as simple as war.”

Sayed Jalal Karim, Afghan diplomat and former ambassador to Saudi Arabia

“I think the intention that the U.S. had was a good intention, because the 9/11 attack was a horror to all. I believe that the overall war against terrorism is a justified cause.  

“But merging terrorism with religion was the biggest mistake I think that was made. We created enemies which were not there.”  

Cole T. Lyle, former U.S. marine and Afghanistan war veteran and former military advisor to Senator Richard Burr

“In the past twenty years, we’ve re-learned that the U.S. military cannot be defeated at the tactical or, with rare exceptions, the operational level of warfare. But the United States can be defeated at the strategic one.

“Foreign and defense policymakers in DC need to start thinking longer-term about America’s strategic interests globally instead of choosing what is in their best interests short-term. The American people need to demand that their elected representatives have a firm grasp on strategic end-states in any major conflict going forward.”

Tracy Walder, former officer of the CIA’s Counterterrorism Center 

“9/11 forced us to deal with a war of ideas rather than war of people or conquering territory and land. I think we are safer in that we have a better understanding of that. 

“However, we have created some instability in countries because of things that we have done there since September 11. Fragile or failed states are hotbeds for terrorism, and I do think that we have created new hotbeds as a result of that.”

Bakos

“I think we’ve ebbed and flowed as far as safety. The U.S. government has caught people planning attacks and stopped them before they’re able to take action, since 9/11. 

“I do think in some ways we are safer, I think in other ways our actions have created obviously a lot more chaos and harm and — ISIS. I mean, let’s be realistic, we would not have ISIS had we not invaded Iraq. We wouldn’t have al-Qaeda in Iraq.”

Karim

“I do not believe that we are more unsafe now, but we could have been in a much better position, if we had balanced the fight against terrorism from all different aspects — education, economy, mentality, instead of only military — and not merged terrorism with religion.”

Patey  

“It manifestly has been safer for the United States where they have not had a serious terrorist attack in the mainland United States for 20 years.

“But Europe and the Middle East have seen more terrorist attacks … The threat has now dispersed across the world.

“We’ve got better intelligence defenses; it’s much more difficult for terrorists to mount complex attacks of the sort that 9/11 was … but this ideology is still able to produce homegrown people willing to do unspeakable things. And indeed, the Taliban takeover of Afghanistan will probably have encouraged these people.

“The nature of the threat has changed – it’s less concentrated and more dispersed all over the world. The (radical Islamist) franchise is alive and well.”