A BLUE, cloudless sky in late summer. From the west, almost in slow motion, a plane – it’s impossible to tell at this stage if it’s small or large because of the foreshortened perspective through the long lens of the camera – swoops in low and explodes against the steel skyscraper, sending out dense puffs of flames, oil-blackened gases and shards of metal.

This is the south tower of the World Trade Centre. The world is already watching because less than 20 minutes earlier another plane had plunged into the north tower.

Now, on September 11, 2001, universally known as 9/11, men and women from the top floors of the 110-storey north building were seen throwing themselves to the ground below rather than be burned alive. The al-Qaeda hijackers had taken over the two flights and piloted them into the buildings.

The first, a Boeing 737, American Airline Flight 11 from Boston, hit the north tower at 8:46:40, impacting between the 93 and 99th floor, instantly killing nine crew members, 56 passengers, and five hijackers as well as hundreds inside.

At 9:03 the second plane, United Flight 175, also from Boston’s Logan Airport, hit the south tower. Forty-three minutes later another flight from Logan, American 77, hit the Pentagon and at 10:03, United 93 crashed into a field near a reclaimed strip mine in Shanksville, Pennsylvania after passengers tried to retake the plane from the hijackers.

This is the chronology of terrorist destruction which left almost 3,000 dead and set off a chain of catastrophic events throughout the world propelled by these 57 minutes of horror.

The US president, George W Bush, was at a school in Florida listening to seven-year-old kids reading The Pet Goat when he was told a second plane had hit the second tower.

It’s not too dramatic to mark this as a day the world changed. There had never been an attack on America’s homeland in 200 years. For Bush, it gave him a new sense of mission with no room for doubts, and it gave rise to a renewed sense of patriotism, misguided or not, but shot through with fearfulness.

It was to be war without end, regardless of cost – one now outdated estimate puts the cost since then at more than $6 trillion, or more than $35 million every hour – and it set off a chain of unintended consequences.

The next day Bush addressed the nation and said the country was at war. Eight days later, Bush was at the US Congress saying: “Our war on terror begins with al-Qaeda, but it does not end there. It will not end until every terrorist group of global reach has been found, stopped and defeated.”

Three weeks later, on October 7, 2001, airstrikes involving US and British planes were launched at al-Qaeda and Taliban training camps in Afghanistan and two weeks later began the ground assault on the country, in a war that is still not properly resolved nearly 20 years later.

In March 2003, following “intelligence” that Saddam Hussein had weapons of mass destruction, the invasion of Iraq began. It was based entirely on invented information that Saddam had WMDs. Here, in the confected, so-called “dodgy dossier”, it was claimed that not only did he have them but was, in Tony Blair’s words, “within a year or two” of having nuclear weapons.

One of the early casualties was Dr David Kelly, a former weapons inspector and senior civil servant, who, following his leaking of information to a journalist, killed himself.

Another of the main premises for the Iraq invasion was that Saddam was harbouring al-Qaeda. Nothing could have been further from the truth. He hated them and brutally extirpated them wherever they threatened to appear.

The invasion quickly overthrew Saddam and his Ba’athist regime, but there was no plan for peace and instead of that a catalogue of crucial errors from ideologues, neoliberals like Paul Bremer, who ran the administration tasked with stabilising the peace. These included disbanding the Iraqi army and banning Ba’ath party members (almost everyone had to be) from civil service and government, which threw hundreds of thousands into penury, and had the opposite and devastating effect. Bremer was last heard of as a ski instructor in Vermont.

In Iraq, it triggered a bloodthirsty and lasting sectarian insurrection, Sunni against Shia, and it also bolstered the regional influence of Iran, now added to the US list of enemies, and fostered the creation of IS, the Islamic State, which took over large swathes of Iraq and Syria for its caliphate.

The terrorism was exported – attacks in London on the Tube and buses, the Bali bombing of 2002, on the Charlie Hebdo offices in Paris in 2015, also the Bataclan theatre as well as outside the Stade de France, although it’s in countries with a large Muslim population that have seen the greatest rise in attacks.

Since 9/11, a wave of Islamophobia was also set off in the West and Muslims in the UK, the US and across the EU have suffered harassment and violence.

Arguably the reaction to 9/11 has eroded civil liberties across the world, countries citing the need to prevent future attacks as justification for increased surveillance, detention of suspects without charge and the general curbing of dissent. It has also badly undermined the intelligence and law enforcement agencies which failed to stop the hijackers despite ample warning,

It would be a mistake to think that US foreign policy changed radically after 9/11. There was no visible break from the past, still the same support for undemocratic regimes in the “national interest”, foreign interventions albeit on a grander scale, extraditions, and torture, although this was denied by Bush’s vice-president Dick Cheney, arguing that using waterboarding couldn’t be called that because it was used on US soldiers during training.

It was no different under Barack Obama. US forces were at war for all of his eight-year term. He dropped more bombs or missiles on more countries than Bush. He launched airstrikes or military raids on at least seven countries: Afghanistan, Iraq, Syria, Libya, Yemen, Somalia and Pakistan and while he cut the number of soldiers in the frontline he expanded the role of special forces – as Osama Bin Laden discovered to his cost – and prioritised the use of new technology, such as drones and cyber warfare.

There’s little doubt that the legacy of 9/11, the demeaning of America, the appeal to patriotism, the fear or hatred of others, the promise to end the the “era of endless wars”, were crucial elements in the success of Donald Trump.

For him, Islamic State was the new target. He famously promised to “bomb the s**t” out of them, and he did, taking it even further, apparently giving the green light to indiscriminate slaughter: “When you get these terrorists,” he said, “you have to take out their families.”

Less than a month after he took office, in January 2017, he escalated the US assault on IS-held Mosul, using drones and heavy weaponry. One intelligence report later asserted that tens of thousands of homes had been destroyed and 40,000 civilians died in the battle in the ruined city.

When they slipped through the derisory security and took over the four airplanes armed only with box cutters, what we’d call Stanley knives, they knew that they were on one final mission. They couldn’t have known, although no doubt would have hoped, that the reverberations of that would continue to this day.