Even as the events of September 11, 2001, were unfolding, the questions people were asking amid the scenes of chaos were an indication that the world was about to change.
Key points:
- Airport security ramped up and CCTV and citizen surveillance became ubiquitous
- The 9/11 attacks fuelled the rise of Islamic terrorism and anti-Muslim sentiment
- Hundreds of thousands of deaths led to the "forever wars" of Iraq and Afghanistan, among other conflicts
"How did a plane fly into the World Trade Center in broad daylight on a Tuesday morning?"
"Twice, in 30 minutes?"
Harrowing images of the 110-storey Twin Towers burning and trapped victims leaping from the buildings were continuously broadcast around the world.
The towers crumbled to dust and, as they fell, they damaged a dozen adjacent buildings and sent debris flying up to 5 kilometres away, across New York City.
It was later confirmed that 19 men, working in groups, had hijacked four separate flights from three different airports, within the span of 45 minutes at what was rush hour that fateful day.
Two planes were flown into the towers and a third crashed into the side of the Pentagon about 30 minutes later.
A fourth plane crashed into a field. Its target remains unclear to this day, but it is believed it was heading for the White House or the Capitol Building.
There were no survivors from any of the flights, and nearly 3,000 people were killed.
Loading...Al Qaeda, a designated terrorist group founded by Osama bin Laden, was quickly blamed for the attacks.
The US responded by launching a "war on terror" and invading Afghanistan, where terrorist training had taken place.
Now, 20 years on, impacts of that time — the war in Afghanistan, the plight of WikiLeaks founder Julian Assange and ongoing threats of terrorist attacks — continue to feed headlines.
Here are three ways the events of that day shaped the world we live in today.
Mass surveillance, security
Before 9/11, removing articles of clothing and electronic devices before boarding a plane — or disposing of bottles of water, cigarette lighters and shampoo — were unheard of.
While X-ray machines and security did exist, they were hardly afforded the same level of attention.
For example, the 9/11 hijackers boarded flights with box cutters and knives, which were allowed on certain flights at the time.
The fact that multiple members of Al Qaeda were able to visit America over a couple of years — even attending flight schools in some cases — and coordinate below the radar, revealed gaping, multi-faceted vulnerabilities in security.
Security and intelligence expert John Blaxland, who was in Washington DC at the time, told the ABC that, until that point, hijacks were about extortion and holding hostages for ransom.
"The idea of using the actual planes as bombs, like a weapon — no-one imagined that," he said.
"Instantly, Washington DC went from being a city relaxed, to being very, very nervous and paranoid."
Just months after the attacks, the US launched the Transportation Security Administration (TSA), a multi-billion-dollar US Homeland Security apparatus that monitors air travel and employs nearly 50,000 security officers.
It resulted in hours-long queues and pat downs now associated with US airports.
Variations of similar security measures and entities soon followed around the world, as did tens of millions of CCTV cameras on street corners in urban areas and in small businesses.
It also led to the adoption of a raft of new security laws and counter-terrorism measures granting surveillance powers to governments.
Counter-terrorism and international policy expert Lydia Khalil said the policy outcomes from the reaction to the September 11 attacks remained with us now.
"There was a real, palpable fear and sense of insecurity that those attacks brought, and we're still living with the impacts of [surveillance powers and counter-terrorism legislation] that was put forward," Ms Khalil said.
"Some of it was necessary, certainly … but then it resulted in a lot of overreach as well.
"And, so, it kind of normalised a lot of today's perceptions around mass surveillance."
In the following years, not only did surveillance and security measures increase, but also sophisticated systems of data collection.
"These developments were inconceivable to previous generations," Professor Blaxland said.
Islamic terrorism, anti-Muslim sentiment
Before 9/11, "terrorism" was not a household term and it was generally reserved for political discussions involving hardline communists or anarchists, such as Ted Kaczynski, also known as the Unabomber.
"Terrorism had been around for a while [in isolated attacks and car bombings], but it was a manageable risk," Professor Blaxland told the ABC.
"It was the industrial scale of 9/11's international terrorism that transformed it from being something you read about in the papers, to being something of fundamental importance to everybody."
Ms Khalil was in her last year of university in Boston at the time of the 9/11 attacks, not far from the airport where two of the planes were hijacked.
She recalls watching it unfold from her dorm room thinking, "This is going to change everything".
"A few months before, I took a foreign policy class looking at conflicts not getting enough attention, and the professor asked, 'Has anyone ever heard of Al Qaeda?' And hardly anyone raised their hands," Ms Khalil said.
Just a year later, such a question would become redundant.
After 9/11, there were waves of terrorist attacks targeting Western cultural centres, resulting in mass casualties: Bali in 2002 and 2005, Madrid in 2004, London in 2005, Sydney in 2014, Paris in 2015 and many, many more.
In the process, the simple utterance of the phrase "Allahu akbar" (God is great) — a religious phrase routinely said by more than a billion Muslims worldwide — would come to be interpreted by many as linked to terrorism.
Hundreds of millions of everyday Muslims continue to feel the repercussions of the Islamic terrorist stereotype, with major international policies becoming hostile towards them, including that of former US president Donald Trump's ban on travellers from Muslim-majority countries.
'Forever wars'
Despite Bin Laden explicitly saying he hoped the attack would drag the US into conflict, and that war was what Al Qaeda wanted, within weeks the US invaded Afghanistan in an attempt to dislodge the Taliban from power and clear out Al Qaeda operatives.
Within 18 months, US forces had also invaded Iraq, chasing claims that former president Saddam Hussein was harbouring weapons of mass destruction.
Australia would be dragged into the same wars in support of its American ally.
Even though some protested against invading foreign countries, the rhetoric of revenge dominated discussions after the 9/11 attacks.
"I honestly can't imagine a scenario in which the United States would not have intervened militarily in some respect in Afghanistan — Iraq, I think is a different story — but certainly in Afghanistan," Ms Khalil said.
A decade after September 11, the Arab Spring exploded in the Middle East.
While it was not directly in response to the attacks, the war in Iraq had served as a catalyst for inspiring the youth in Egypt, among other places, to protest against their own governments for supporting the war.
Those conflicts would eventually lead to hundreds of thousands of casualties, regional instability and millions of refugees, while more than an estimated $1 trillion has been spent by the United States and its allies.
"Revenge is best served cold," Professor Blaxland said, "and if it's not cold, then you are going to make serious misjudgements."
Despite the US declaring — just under 20 years later, on August 31, 2021 — that the war in Afghanistan was over, the troubles and headlines will continue for a new generation that likely does not recall the significance of September 11.
Professor Blaxland said these "forever wars" had now eclipsed the "unipolar moment", when the US emerged as the sole superpower following the Cold War.
"It all happened while we were distracted by chopping off heads of the hydra in the Middle East," he said.
"Even when fighting an enemy without superior technology, they outsmart us, and we stand the risk of never learning the many lessons from our experience of the 'forever wars'.
"Of the trillion dollars spent in Afghanistan and Iraq, what could the United States and the West have built in its place?
"Instead, we have the incredible primal destruction left by an incredibly hubris-struck movement that misread its place in the world, and lost opportunities."