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Last week, the United States marked the 18th anniversary of the 9/11 attacks. That means Americans not born at the time of the attack are now able to join the military, head to Afghanistan, and join the seemingly unending—and global—war that began on that day. It also means more and more people have no memory of that day—including the one in five who have been born since. That’s a lot of time for the terror threat to have changed, even as the United States continues to wrestle with the world made by 9/11. As it happens, ¹ú²úÊÓƵ’s work on terrorism has narrated that evolution—a critical feature of our first two decades. This year, as we celebrate ¹ú²úÊÓƵ’s 20th anniversary, our latest report on the terrorist threat shows just how much has changed, and in surprising and worrisome ways.

First, here’s what hasn’t happened. Eighteen years after 19 foreign hijackers entered the country on temporary visas and killed almost 3,000 people, no foreign terrorist organization has managed to carry out a deadly attack inside the U.S. While domestic perpetrators inspired by Bin Laden’s ideology or its inheritors have killed 104 people inside the U.S., such a number would have seemed wildly optimistic in the wake of the attacks.

Critically, given our current politics, every one of these perpetrators has either been a permanent U.S. resident or a citizen—meaning that while many expected second and third waves of the terrorist threat to come from abroad, the threat has largely stemmed from within America.

There have been close calls. In 2009, a Nigerian armed by al-Qaeda in the Arabian Peninsula and trained in Yemen almost brought down an airliner over Detroit; in 2009, three Americans who trained with al-Qaeda in Pakistan returned to the U.S. with a plot to bomb the New York City subway; in 2010, a Pakistani-American who trained with the Pakistani Taliban left a car bomb that failed to detonate in the middle of Times Square.

The rise of ISIS sparked fears that the U.S. had run out of luck as thousands of Westerners flowed to Syria to join the so-called Islamic State. Now, five years after the group declared itself to be the caliphate, ISIS has not directed a single deadly attack inside the U.S.—nor has any returnee from the Syrian conflict committed an attack. Only one returnee is known to have plotted an attack inside the United States.

ISIS did bring a new form of terrorist threat to the U.S. Of the 104 people killed in attacks inspired by jihadist ideology since 9/11, more than three-quarters have been killed since ISIS burst onto the global scene in 2014, and more than half of all deadly jihadist attacks since 9/11 have been ISIS-inspired. This threat is partially rooted in the development and spread of communications technologies and online media platforms that didn’t exist at the time of the attacks—an evolution tracked by ¹ú²úÊÓƵ as we studied the impact of social media on violent extremism, building resilience to it, and how it will impact the future of war.

The threat may be declining as ISIS’s brand suffers due to loss of territory. It has been more than a year since the last deadly jihadist attack in the U.S. Even so, individuals have continued conducting ISIS-inspired attacks: Sayfullo Saipov’s deadly vehicular ramming in Manhattan occurred in the same month that ISIS lost its self-proclaimed capital of Raqqa, and an attempted vehicular ramming in the Washington, D.C. area came while the U.S. Central Command was celebrating the territorial destruction of ISIS.

In addition, a new threat is gaining prominence. Individuals inspired by far-right ideologies have killed 109 people inside the U.S. since 9/11, and in the past few years, there have been a number of particularly deadly attacks: The shooting in El Paso, which was motivated by white supremacy and anti-immigrant views, constitutes the deadliest far right terrorist attack in the post-9/11 era. Nor is far-right terrorism the only threat—the U.S. has seen deadly violence motivated by other ideologies, including ideological misogyny and a range of more idiosyncratic motivations.

The terrorist threat looks very different than it did on September 11, 2001. In some ways, the differences are positive, reflecting a more secure America that has seen far less terrorist violence than was expected nearly two decades ago. In other ways, the threat is increasingly varied and complex—and countering terrorism over the next decade will require adaptation and understanding of today’s environment. Meanwhile, in Afghanistan, Somalia, Yemen, Iraq, Syria, and Libya, U.S. counterterrorism wars sparked in the aftermath of the 9/11 attacks and the rise of various al-Qaeda affiliates continue. Much has changed, but the past is still with us.