How Has the Terrorism Threat Changed Twenty Years After 9/11?

How do al-Qaeda and its affiliates currently pose a threat to the United States and the rest of the world?

The al-Qaeda of today is nothing like it was on 9/11. Its founder and leader, Osama bin Laden, is long dead. With the notable exceptions of Ayman al-Zawahiri, a surgeon turned terrorist and the movement’s current emir, and Saif al-Adel, a former Egyptian army officer and al-Zawahiri’s most likely successor, every single senior al-Qaeda leader has been killed or captured. Seven of the movement’s top commanders have been eliminated since 2019. Today, al-Zawahiri himself is said to be in poor health.

But the ideology and motivation espoused by al-Qaeda is, unfortunately, as strong as ever. For instance, there are now four times as many Salafi-jihadi terrorist groups designated by the U.S. State Department as foreign terrorist organizations than there were on 9/11. And the most recent report from the United Nations’ monitoring team [PDF] points to al-Qaeda’s unimpeded growth in Africa, entrenchment in Syria, and presence in at least fifteen Afghan provinces, as well as its continued close relations with the Taliban.

Americans also shouldn’t be lulled into thinking that al-Qaeda no longer wishes to attack the United States. The 2019 attack by a Saudi sleeper agent at a U.S. Navy air base in Pensacola, Florida, which killed three people and wounded eight others, was a reminder that al-Qaeda is still able to mount international terrorist operations by working through one of its dedicated, highly capable franchises—in this case, its Arabian Peninsula affiliate.

What were the greatest successes and failures of the U.S. counterterrorism response of the past twenty years?

The number one success was the government’s thwarting al-Qaeda’s every attempt to carry out another attack in the United States on the scale of 9/11—although the 2019 Pensacola shooting was an important warning against becoming too complacent.

The worst failure—beyond any doubt—was the 2003 invasion of Iraq, which diverted critical resources away from efforts to finish al-Qaeda off in South Asia during the best window of opportunity. The invasion also inadvertently set off the chain of events that led to the emergence of the self-proclaimed Islamic State, an even more violent and unconstrained version of al-Qaeda. It took an eighty-three-country coalition some five years to defeat the threat posed by the Islamic State.

During that period, the Islamic State executed and inspired deadly attacks on civilian targets in cities including Brussels, Nice, New York City, and Paris. The al-Qaeda splinter group also conducted the first successful terrorist attack in over a decade against a commercial aviation target, killing 259 people flying from Egypt to Russia. It also changed the nature of modern terrorism by pioneering the use of social media for recruitment, propaganda, and to encourage totally independent, lone-wolf attacks.

In the worst category, it must also be said that in the course of responding to the events of 9/11 and in seeking to defend the country from further attacks, the U.S. government abased some core American values and principles of justice. For instance, imprisoning people for decades without trial is something that the United States has always criticized nondemocratic governments for. Yet, several dozen detainees remain at the U.S. detention facility at Guantanamo Bay, many held indefinitely without charge. Similarly, the detainee abuse that occurred there, at CIA black sites, and at Abu Ghraib prison in Iraq tarnished the United States’ reputation and generated worldwide condemnation.

The U.S. national security apparatus transformed significantly post-9/11. What were the most significant changes?

The vast counterterrorism bureaucracy created in the aftermath of the 9/11 attacks was the biggest and most enduring change. For instance, a 2010 Washington Post investigation revealed the existence of a vast counterterrorism archipelago of some 1,271 government entities and 1,931 private companies focused on counterterrorism. The war on terrorism also entailed increasing the number of people with top-secret security clearances to an estimated 854,000 and constructing more offices and secured facilities to accommodate them—an expansion equal to “almost three Pentagons or 22 U.S. Capitol buildings—about 17 million square feet of space.”

But in securing and protecting any country from terrorist attack, a perennial question is how much is enough. As the above data implies, the United States potentially overreacted to the 9/11 attacks by creating redundancies or granting sweeping powers to various agencies. At the same time, it is indisputable that U.S. counterterrorism measures have succeeded in preventing anything like 9/11 from occurring again. The challenge going forward, especially at a time of competing national security challenges and diminished fiscal resources, is finding and maintaining a prudent balance in guarding against the terrorist threat while attending to other, perhaps more pressing security priorities.

What are the main terrorist threats to the United States today, and what lessons does the 9/11 response provide for combating them?

Sadly, the terrorist threat to the United States has shifted from a mostly external one—which it was for nearly two decades after 9/11—to an internal one, as the Capitol Hill riots of January 6, 2021, highlighted. But the ongoing threats posed by the Islamic State and al-Qaeda have not disappeared.

The challenge for the United States will be formulating a sufficiently agile and ambidextrous counterterrorism capability to defend against the full array of terrorist threats—both foreign and domestic—that will surely persist. Both the 2018 National Strategy for Counterterrorism and the first-ever National Strategy for Countering Domestic Terrorism, released in June 2021, provide clear exegeses of the holistic approach needed to protect the country from terrorism.

However, the bitter partisan divisions that exist in the United States today could undermine the implementation of a coherent counterterrorism strategy. The unity, common purpose, and shared destiny that drew the country together after the 9/11 attacks no longer exist. In contrast, the current climate of political polarization could effectively paralyze the government in preparing for the next generation of threats.