“I’m now the fourth American president to preside over war in Afghanistan—two Democrats and two Republicans,” President Biden said during his speech on August 16. “I will not pass this responsibly on— responsibility on to a fifth president.” He needn’t have corrected himself. He did indeed irresponsibly bequeath to his successor a terrible situation in central Asia.

The best-case scenario, according to Biden, would look like this: Afghanistan’s reversion to Islamofascism fades from the international headlines. The Taliban understands that its continued rule depends on its ability to prevent terrorists from launching attacks from its territory. America goes back to fighting over masks and vaccinations and “building back better,” or whatever.

But the best-case scenario is an illusion. Why? Because the war isn’t over. Afghanistan is just one front in a global conflict that the United States did not initiate and cannot wish away. The Cold War did not end when the South Vietnamese government collapsed. Nor will the war on terror or the “Long War” or the “Forever War” cease with Taliban control of Afghanistan. When participants in the worldwide Salafist-jihadist movement look at the developments of the last week, they don’t see reasons to quit their mayhem. They see the chaos, panic, violence, disorder, and American retreat as a vindication of their ideology and a spur to further action.

It’s happened before. North Vietnam’s victory over the South did not make communism less expansionist or revolutionary. On the contrary: Laos fell to the Communists, Cambodia was subjected to the barbarism of the Khmer Rouge, Cuba sent advisers to the pro-Communist People’s Movement for the Liberation of Angola, the Sandinistas overthrew the anti-Communist Somoza dictatorship in Nicaragua, the Soviet Union invaded Afghanistan, and a pro-Communist insurgency took root in El Salvador. The relentless humiliations that followed America’s defeat in Vietnam ended Jimmy Carter’s presidency. They did not stop until Ronald Reagan shifted the nation’s course.

Or try a more recent example. When America removed its troops from Iraq at the end of 2011 and failed to enforce its red line against the use of chemical weapons in Syria in 2013, the Middle East did not become less violent or pathological or dangerous. It was only a matter of time before ISIS overran the Iraqi cities of Falluja, Ramadi, and Mosul. On June 29, 2014, the terrorist army’s leader, Abu Bakr al-Baghdadi, announced the formation of a caliphate. Then ISIS moved toward Baghdad and enslaved and massacred Iraq’s Yazidi population along the way.

So terrible was ISIS that in August 2014 President Obama intervened against it with airstrikes—an intervention that continued, with greater success, under Obama’s successor. As I write, the caliphate is no more, Baghdadi is dead, and Iraq has another shot at a better future. There are 2,500 U.S. troops in Iraq and some 900 in Syria. This is not a coincidence.

How long, then, before U.S. forces return to Afghanistan? I recognize that it might feel a little silly to ask such a question at this moment. Biden already has deployed more troops to Afghanistan to evacuate civilians than were there when he gave the order to leave. Let’s say, though, that the withdrawal is completed without incident—a questionable assumption—and that there are no Americans in Afghanistan by the 20th anniversary of the September 11 terrorist attacks. What happens next?

The first thing to note is that the Taliban faces rebellion. Demonstrations against the return of the Islamic militia have been met with violence. They may increase in number. Meanwhile, the son of the late Ahmad Shah Massoud, the legendary anti-Taliban mujahid who was murdered two days before 9/11, has announced the renewal of his family’s resistance campaign. Just as the Taliban never surrendered after the U.S. intervention, neither will the former partisans of the Northern Alliance acquiesce to the collapse of Kabul. Afghanistan is too geographically and ethnically diverse to submit easily to the domination of one party.

Even a low-grade civil conflict will draw in other powers. The list of interested parties begins with nuclear-armed Pakistan and includes Iran, Russia, China, and India. America will be forced to pay attention and likely will become involved. After all, the fate of Afghanistan is part of the “great power competition” that President Biden said he cares about.

Biden also said he’s “adamant that we focus on the threats we face today in 2021—not yesterday’s threats.” And the “terrorist threat,” he went on, “has metastasized well beyond Afghanistan.” He didn’t acknowledge that one of the reasons the threat spread out of Afghanistan was that for 20 years America denied it a base there. Now that the Taliban is in, and the Americans are out, the elements of al Qaeda and ISIS in Afghanistan today will be joined by more holy warriors.

Not to worry, though, said Biden. “We conduct effective counterterrorism missions against terrorist groups in multiple countries where we don’t have a permanent military presence.” And we can do the same thing in Afghanistan, he continued, because “we’ve developed counterterrorism over-the-horizon capability that will allow us to keep our eyes firmly fixed on any direct threats to the United States in the region and to act quickly and decisively if needed.”

Let’s hope he’s right. The problem with his argument is that America does have a “military presence” in north and east Africa, Syria, and Iraq, as well as in Turkey, Kuwait, Qatar, Jordan, and elsewhere. And America does have a naval presence in the Mediterranean, Persian Gulf, and Indian Ocean. Our eyes are “firmly fixed” on bad spots in the Middle East and North Africa because we are nearby. The horizon over which our counterterrorism forces must travel is short. That won’t be the case in Afghanistan.

Biden created a situation in which America has neither boots nor eyes on the ground in a landlocked, mountainous country thousands of miles from port and surrounded by unfriendly states. Unlike 20 years ago, China and Russia are strong and adversarial and looking for opportunities to embarrass the United States. Every threat or attack that emanates from Afghanistan will testify to U.S. stupidity and weakness. Furthermore, the Taliban, even as it is dogged by internal opposition, will command more territory and field stronger forces than any of the Salafist-jihadist outfits scraping by in the ungoverned and contested spaces of the Maghreb, the Sahel, the Levant, and the Arabian Peninsula. Our intelligence capabilities will be hobbled and our response time lengthened.

This dispiriting assessment doesn’t include the propaganda boon to the Salafist-jihadist cause. Kabul will be transformed from an island of modernity to the global capital of anti-Western jihad. International terrorism flourished alongside the Islamic State. It manifested in spectacular, mass-casualty attacks in Paris, Marseilles, San Bernardino, Orlando, and Manchester. “For a long time now Islamist movements have defined the creation of an ‘Islamic state’ as their goal and standard for achievement,” writes former State Department official Charles H. Fairbanks. “A state provides a better terrorist sanctuary, and has far more versatile capabilities, than a movement.” A state gives a movement safe harbor, institutional support, and physical inspiration for “lone wolves” in the West to murder unbelievers. Such a state is what the Taliban will build in America’s place.

“I made a commitment to the American people when I ran for president that I would bring America’s military involvement in Afghanistan to an end,” Biden said. “And while it’s been hard and messy—and yes, far from perfect—I’ve honored that commitment.” Yes, he has. The Taliban’s military involvement in Afghanistan, however, continues in our absence. And so the Afghan people are left to suffer, the world watches agog, and America is vulnerable to resurgent Islamic extremism. The Forever War isn’t over—it’s entered a new phase. Where the enemy has the upper hand.

Matthew Continetti is a resident fellow at the American Enterprise Institute and the founding editor of The Washington Free Beacon. For more from the Free Beacon, sign up free of charge for the Morning Beacon email.