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

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.

Bruce Hoffman is the Shelby Cullom and Kathryn W. Davis Senior Fellow for Counterterrorism and Homeland Security at CFR.This article is published courtesy of the Council on Foreign Relations (CFR).