THOSE of a generation older than me were shaped by the assassination of John F Kennedy. Parents, teachers, relatives and neighbours could remember where they were and what they were doing when they heard the news. It was a day of collective outrage, shock and mourning, and so often retold it felt as if we had all witnessed it for ourselves.

For the present age, our pivotal moment was 9/11. Its impact dwarfed that of JFK’s murder, because it was an attack on us all. Almost 3000 died and over 6000 were injured on that dreadful day, but as its significance sank in, everyone in the West knew they too had a target on their forehead.

Who could ever forget, as word spread, rushing to the nearest television, to watch footage of the first plane flying into the North Tower of the World Trade Center? When it was followed by a second, tearing into its twin, a sickening sense of dread set in. Crammed into a small room around the screen, colleagues in my office gasped or shouted. Some started to cry.

And that dread, while no longer as intense, has yet to disappear. The sight of this attack, and the apocalyptic collapse of the towers, was a moment of profound horror. For those of us in Europe, almost as much as in America, it became obvious that our world and our way of life had, in an instant, been fundamentally changed.

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Obviously we could not foresee the conflicts, wars and killings that would come in the wake of the worst terrorist act in history. But you didn’t need to be a politician or military strategist to know that a new and frightening era had begun. The fact that it had started many years earlier, with other suicide bombings and ambushes by al-Qaeda, only gradually dawned. The evil genius of the co-ordinated airplane strikes on September 9, 2001, was that the spectacle of doom, arriving out of clear blue skies, struck terror into the heart of the West. As it was intended to do.

Political leaders charged into battle. Yet for ordinary people, who were not part of the rescue operation, or called to military action, nor on the front line of medical and charitable work, 9/11’s impact was nevertheless profound. There was no period of phoney war, when we wondered what all the fuss was about. Straight away we were pitched into an environment where it seemed attack might arrive in any shape, from any corner, at any time. Even the once-benign sight of planes passing high overhead became a reminder that mortal danger could come from above.

Some days after the attacks, a friend’s son was on the first flight out of New York to the UK. When he reached the airport there was a bomb scare, which did nothing to calm nerves. You can only imagine his feelings on boarding the aircraft, wondering if he would make it across the Atlantic. Most of us had similar thoughts when we next took a flight, or got on the Tube, or stepped into a lift heading for the 20th floor.

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This was what was so fiendish about al-Qaeda’s tactics. They undermined confidence in everything around us. No matter how impressive or solid a building, they could reduce it to dust. And over the following months and years, they underlined that message, carrying out countless atrocities. Some made bigger headlines than others: the Madrid railway explosions, the London bombings, the Charlie Hebdo shootings. But the number of attacks in the Middle East far out-numbered those in Europe.

On the heels of fear came suspicion. Anti-Muslim sentiments began to fester, a poisonous legacy we are still dealing with. Instead of uniting, people splintered into Us and Them. This made the day-to-day life of Muslims, or those of other minority ethnic backgrounds, a great deal harder.

But while some nursed their prejudices, others realised it was time to learn more about politics and people beyond our borders, to broaden their understanding. In so doing, they started to see the West from a different perspective.

To the initial flood of books, films and TV series with anti-terrorist plots were added novels, memoirs and eye-witness accounts illuminating what it was like in war-torn Afghanistan, Iraq or Syria, or the many other countries where conflict raged.

In all of these regions, the West’s unthinking sense of moral authority was constantly challenged. As we watched an escalation of terrorist activity under new names, we also adjusted our historical lens. I can’t speak for others, but for me the aftermath of the attacks included a growing awareness of the far-reaching, complicated and pernicious web of geopolitical ambitions and connections – 9/11 was the day that illusions died, and scepticism took root.

At the same time, the world shrank. No-go regions proliferated. Even heading to supposedly safe destinations we became inured to endless security checks. Do they make us feel better protected? Probably. But they also reinforce how vulnerable everybody is. And while their tedium has been factored into how we travel, so has a low-level but persistent anxiety. It’s the psychological equivalent of tinnitus – a faint but ineradicable sensation of knowing the worst could happen at any moment.

The ramifications of that day spread further than any individual’s fears. Our current shortage of HGV drivers, fruit pickers and hospitality staff can be traced to the hour the towers fell. Insidiously, as radical Islamism gathered pace, parts of the British community began to yearn for old securities, to return to the supposedly golden age of being a self-sufficient island nation. Brexiteer propaganda played to mistrust of foreigners whose ethnicity or appearance reminded some of Osama Bin Laden, Isis or the Taliban. As a result, Britain as a whole voted to pull up the drawbridge, even if Scotland did not.

Twenty years on, we are still living with the fall-out from 9/11: the supermarket’s empty shelves, the restrictions in what we can pack for holidays, our hyper-vigilance when in crowded places, where an abandoned rucksack no longer looks like carelessness but a potentially mortal threat.

Recently, Tony Blair suggested that the next wave of radical Islamist terrorism might involve biochemical warfare. On that miserable, sunny September day we caught a glimpse of the future. It’s as alarming now as it was then.

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