In the past few weeks sad moments and memories of yesteryear have been inescapable as we have watched disaster unfold in Kabul, triggering time and again images of 9/11. Think about those two young men falling from the under-carriage of a C-17, accompanied by thousands of Afghans so desperate to escape. Then recall the memory of people jumping from the burning windows of the Twin Towers on a Manhattan morning twenty years ago.

Yet there is one big difference, twenty years on: back then, our world was united about what came next.

The terrorism of twenty years ago has spawned tragedy all its own

See the final TV address of Afghanistan’s last President, Ashraf Ghani, as the Taliban closed in on Kabul, barely able to look at the camera as he encouraged citizens to stand firm, masking all the while that he was about to flee the country himself. Then ponder the face of George Dubya Bush, hearing the news of the 9/11 attacks, whispered in his ear, as he sat in a schoolroom in Sarasota, Florida, reading stories to kids, that September morning.

Finally, remember the image that will become iconic out of Kabul from this period: a US soldier taking a tiny kid from a very relieved parent over the barbed wire at the airport. Then recall the New York firefighter, his face caked deep in dust, escorting a crying mother from the World Trade Centre. The terrorism of that tragic, late-summer morning twenty years ago has spawned tragedy all its own two decades on.

The difference is that we see the tragedy today, but not the need to act in unison.

What a contrast between then and now. In how the immediate aftermath of 9/11 played out, in the frantic days after Jihadist hijackers turned airliners into weapons of mass destruction, going west out of the east coast, taking the lives of so many not just on board but those on the ground in New York and Washington, D.C. It’s hard to remember now, but the world at large reacted with a unity unthinkable today, given the deep divisions over the exit from Afghanistan.

The day after 9/11, the Security Council of the United Nations passed a historic resolution, number 1368, effectively giving Washington and its allies the green light to go into Afghanistan to destroy Osama Bin Laden and al-Qaeda. The language was carefully couched, typical of the UN and the Council, expressing “readiness to take all necessary steps to respond to the terrorist attacks of 11 September 2001”. There were no naysayers. I recall the Bush White House and Tony Blair’s Downing Street terming it “the watershed decision, the go-ahead for invasion and war”. That’s what it was.

Even Latin America looked promising, with reforms replacing old dictatorships

The NATO alliance in Brussels then followed, triggering Article Five for the first time in its history, the clause that signals when the European allies are willing to go to war. That momentous week brought the coup de grace from Paris. In the words of Le Monde newspaper: “In this tragic moment, when words seem so inadequate to express the shock people feel, the first thing that comes to mind is this: We are all Americans!”

I’ve been thinking about that moment, when we White House Correspondents were briefed on President Bush’s determination, the leader himself telling his aides: “We will take the bastards out wherever they are, even the French agree.” Not even the Russians or the Chinese could argue with that.

I have a Washington colleague from those days who sees that period as the high-water mark for Western democracies, the window of opportunity to hold terrorists to instant justice and tyrants in check, support the cause of freedom and shape global events. He has a long list of what we in the West had going for us: by the millennium the West had subdued the Russians, absorbed much of the old Soviet empire into our western alliances, put Saddam Hussein in a box after Iraq’s invasion of Kuwait, made peace with Vietnam and forged new relationships in Africa. Even Latin America looked promising, with economic and democratic reforms replacing old dictatorships.

I remember, in the days leading up to 9/11, visiting Mexico to see a newly-installed President — one Vicente Fox — and hearing him brimming with confidence that his government and the Bush administration could agree on immigration reforms that would work for both, and finally solve the endless war of words along that border on the Rio Grande (consider the enormity of that problem twenty years on). “We have such opportunities to exploit for the benefit of all,” Fox told me back then. “Stop seeing conflict, see conflict resolution.”

My colleague insists Jeffersonian diplomacy was never the goal

Heady days, heady words. The temptation is to fast forward twenty years, and see the inheritance of 9/11 as having been squandered by the Bush/Blair double-act that took us to regime change in Iraq, and so diverted the West from the project that was Afghanistan on 9/12. That’s a tad simplistic. What’s self-evident is that our leaders seriously over-reached, thought military might would triumph and blessed themselves with the semi-belief that they were doing God’s work.

What hurt most was the size of the West’s ambition in Kabul. How, truly, do you nurture a democratically-guided federal state in a country of 14 different ethnic groups, three competing strains of Islam, a per-capita income of scarcely $500 a year and a long history of organizing pocket militias to settle scores along tribal lines? My colleague insists Jeffersonian diplomacy was never the goal, rather the belief that the Afghans were as capable as anyone of electing their own leaders, given the chance. Point taken. Oh, and by the way, was it wrong to educate girls, and empower adult women, to have a major role in the future of their country? No, of course not.

But where to go from here? Well, for a start we need to remind the Taliban that they inherit a country in desperate straits, facing hunger, poverty and disease unless they seek aid from a wider world that wants to see their actions, not their words. We must use any such aid — unashamedly, blackmail is the word that comes to mind — to advance the cause of women and human rights. As for harbouring terrorists, for once might is right, even if it’s a drone as killing machine these days. The Taliban can choose to go their own way, but the price will be huge. And they will pay it, now that they are the Government.

Come this haunting 20th anniversary of that morning in Manhattan and Washington, D.C. and Shanksville, Pennsylvania, where United Airlines Flight 93 crashed after passengers fought the hijackers, maybe it’s worth considering how united our world was in the aftermath of 9/11. Because what the Taliban surely needs to hear now is one voice, in the name of humanity, not many in the name of national interest.