As the post-9/11 chapter closes, a new one begins, marked above all by the end of American deterrence and the eclipse of American power.

Our total defeat and ignominious, disastrous withdrawal in Afghanistan, after 20 years of war and nation-building, closes a chapter on post-9/11 America — and opens another.

What comes next is to some extent uncertain, but you don’t need to be a grand strategist to see the broad outlines of what is already taking shape.

First and most obvious, Afghanistan will revert to being a terrorist haven. The Islamic Emirate of Afghanistan, by its very nature, will not keep to itself, the erstwhile assurances of Taliban officials notwithstanding. Every committed jihadist on earth who can get to Afghanistan is headed that way now or making plans to do so.

Our military leaders have already admitted as much. Two weeks ago, well before the suicide bombing attacks that took the lives of 13 American soldiers and scores of Afghans, the Pentagon told U.S. senators that the collapse of the Afghan government and the Taliban takeover means terrorist groups will reconstitute in Afghanistan more quickly than was previously estimated.

On an August 15 phone call with top Biden officials and senators from both parties, Chairman of the Joint Chiefs of Staff Mark Milley said the previous assessment, back in June, was that there was a “medium” risk that terrorist groups would form in Afghanistan within two years of the U.S. withdrawal. Asked if he believed that timeline would have to be moved up in light of recent events, Milley reportedly responded, “Yes.”

In practical terms, this means in the years to come we’re almost certainly going to see a resurgence of Islamist terrorism worldwide, and likely another attack on American soil. Why? Because for al-Qaeda, and for jihadists the world over, the Taliban’s victory in Afghanistan is a vindication of 9/11, a strategic victory. After 20 hard years, they won and we lost.

Osama bin Laden predicted something like this would happen. Not long after the U.S. invasion of Afghanistan, bin Laden issued a “letter to the American people,” in which he declared that, like the Soviet invasion of an earlier generation, the Americans would eventually leave in defeat:

If the Americans refuse to listen to our advice and the goodness, guidance and righteousness that we call them to, then be aware that you will lose this Crusade Bush began, just like the other previous Crusades in which you were humiliated by the hands of the Mujahideen, fleeing to your home in great silence and disgrace. If the Americans do not respond, then their fate will be that of the Soviets who fled from Afghanistan to deal with their military defeat, political breakup, ideological downfall, and economic bankruptcy.

Bin Laden and those who planned 9/11 recognized the U.S. invasion of Afghanistan for the strategic error it has proven to be. All of them understood the collapse of the Soviet Union as a direct consequence of the USSR’s failed invasion and occupation of Afghanistan, and credited the mujahadeen with the collapse of the communist superpower. It might take time, they thought, but the same would happen to the United States should it be foolish and arrogant enough to invade and occupy the country. And we were.

For all that, a Soviet-style collapse of the U.S. won’t happen. But our humiliation in Afghanistan will have global reverberations. The military power of the United States was the last institution of public life Americans really trusted, and it was the foundation of other nations’ trust in us — or fear of us.

Our adversaries will react accordingly. China, above all, will understand our defeat in Afghanistan as the end of American deterrence and a chance to press its irredentist agenda in Taiwan and the South China Sea. Moscow and Tehran will come to similar conclusions, as will Pyongyang.

Indeed, over the weekend, the Wall Street Journal reported that North Korea has resumed operation of its plutonium-producing reactor at Yongbyon, which had been inactive since December 2018. The operation of the reactor has apparently coincided with signs that North Korea has also begun to separate plutonium from spent fuel previously removed from the reactor.

For our allies, the end of American deterrence will likely prompt a strategic recalibration. Why would Taiwan, which this week issued a dire warning that China’s armed forces could “paralyze” Taiwan’s defenses, put its faith in an alliance with the United States? Why would Ukraine or Poland?

As we learn more in the coming weeks and months about the fecklessness and deceit of the Biden administration’s Afghanistan withdrawal — including Biden’s appalling conversation with then-President Ashraf Ghani, urging him to “project a different picture” of the fight against the Taliban, “whether it is true or not” — every nation in the world will take note of what our promises are worth.

Some of these developments will take decades to mature, but others will move rapidly. By the end of Biden’s term, assuming he’s able to see it through, we might well long for the days when all we had to worry about was our humiliation in Afghanistan. We’ll certainly come to see the events of the past few weeks in a stark new light: as the beginning of a dark chapter in world history, marked above all by the eclipse of American power and influence in an increasingly dangerous world.