In the afternoon of September 11, 2001, stupified Europeans watched as the US suffered the world's most lethal terror attack.
The plane hijackings may have targeted the US and some of its most symbolic buildings — the Twin Towers in New York and the Pentagon — but their repercussions were felt worldwide.
The attacks, at the turn of a new century, brought sweeping changes in travel, security and immigration.
Here's how it all affected Europeans.
Security at airports
The first, most immediate and tangible change for citizens around the world, including in Europe, took place at airports. Few may remember what it meant to fly without having to wait in a long queue at the security checkpoint, but twenty years ago boarding a plane was nothing like it is today.
Just two months after the attacks, then-US President George W. Bush signed a law creating the Transportation Security Administration, a body of federal airport screeners to replace the private companies that airlines hired to handle security.
Thus began the multiplication of airport security measures around the world.
Passengers were banned from bringing more than 100 millilitres of the same liquid onto the plane, asked to submit to random baggage checks, have their personal belongings scanned, and remove their belts before walking through a metal detector.
Later that year, an attempt by British citizen Richard Reid to bring down a plane from Paris to Miami with a bomb hidden in his shoe, led to shoes also being scanned.
Migration policies and xenophobia
The attacks against the US, carried out by al-Qaeda, also led to the criminalisation of immigrants, especially those from Arab and Muslim-majority countries, say experts
For Alejandro Velez, a researcher at Barcelona's Pompeu Fabra University and author of a doctoral thesis entitled "Effects and consequences of 9/11: an ethnopolitical perspective", the attacks on 9/11 offered governments "a perfect pretext for the strengthening of these kinds of policies that began to be applied indiscriminately".
And so, politically, immigration "began to be understood in terms of security, rather than humanitarian issues," Velez said.
"If you look, in depth, at all of (the European Border and Coast Guard Agency) Frontex's projects, there are many, many in which it is precisely to use technology to prevent migration, both through the Mediterranean and through the forests that divide countries like Bosnia, Hungary or the border with Turkey," he added.
Marc Helbling, professor of political sociology at the University of Bamberg, in Germany, and co-author of the "Terrorism and Migration: An Overview" study, concurred.
"There is a lot of research that shows that people perceive immigration in general as a danger to their culture or their economic situation, and obviously a threat can also refer to security issues where they fear for their lives or their society."
Terrorist attacks, especially those committed by people with an immigrant background, "should then lead to more prejudice and negative attitudes towards migrants," he said.
The increase in xenophobia and Islamophobia immediately following an Islamist terror attack, however, tends to be short-lived, according to Helbling. However, Muslims' reports of stigmatisation can be explained by the fact that "attitudes are already negative amongst certain groups of the population before and have become more negative over the last decades."
Difficulties for Arabs and Muslims
Saki Ahadi, born in Afghanistan and resident in Germany since his teenage years, exemplifies how these attitudes have translated into the lives of migrant communities in Europe.
At 19, he was employed as a trainee at a company operating out of Munich airport.
"I didn't have a German passport yet, and when I presented my Afghan passport, it raised a lot of questions and fear," he told Euronews. For several weeks, his documents and background were checked.
"It's quite a strong feeling, not being able to go to work because of your origins," he said.
A few years later, a short trip to London with his brother and a friend also proved difficult to organise. They submitted visa applications to the British embassy. His was processed quickly but his two companions were not so lucky and were asked to visit the embassy in Düsseldorf for an interview. There, they were asked dozens of questions, most of them related to terrorism, including: "Do you know organisation X, do you have contacts with organisation Y?"
Their applications were rejected with the British embassy labelling them "a potential danger".
"I flew alone," Ahadi said. "That was very sad."
Attending the US to do a five-month internship was also a headache. He had to submit a CV listing, with proof, every single country he had travelled to or lived in — not an easy feat for someone who fled Kabul as a child and lived in several countries as a refugee.
The US embassy asked him to answer plenty of questions to ascertain whether he had ever been in contact or donated money to a terrorist organisation.
"After about seven weeks, I was invited to the embassy and my visa was approved. Seven weeks of anxiety for a five-month internship. It was quite an event," he said.
A far-right resurgence
The notion of the other as an enemy is not particularly new in the political discourse.
The attacks on 9/11 had "a profound effect on political debates and political discourse," as have the wave of terror attacks in Europe since then, Helbling told Euronews.
"You clearly find a strong effect of these attacks and that also lead to the emergence of the far-right or, you know, the additional electoral success of the far-right," he went on.
In general, the party in power tends to be punished at the ballot box following an act of terrorism while "the political right profit from attacks", he said.
More recently, this fear of the other has been exploited by Donald Trump in the US — who tried to implement a Muslim travel ban and build a border wall with Mexico — or by Jair Bolsonaro in Brazil.
In Europe, several far-right parties have benefitted from the migrant crisis including Spain's Vox, Viktor Orban's Fidesz in Hungary or Matteo Salvini's League in Italy.
"We are in an era in which the politics of the war on terror is being combined with post-truth, and this has also reached Europe, with extreme right-wing parties stirring up this fear of the other," Velez pointed out.
The end of privacy?
The attacks against the US also led to a decline in individual privacy.
"After 9/11 nothing was ever the same," Catarina Frois, senior researcher at the University of Lisbon's Centre for Research in Anthropology, told Euronews.
"In a way, the decisions taken in the United States, especially in the context of the Patriot Act, determined the behaviour of all countries in terms of security and surveillance. What happened is that they created a new world order in terms of security policy adopted by the States.
"There were no more boundaries, in practice (...) and so the common good actually came to override individual freedom at all levels. And that was one of the main transformations," she explained.
Velez highlighted that "in the United States and elsewhere in Europe, such as in the United Kingdom, regulations (were introduced) that allowed to tap communications, not only by telephone, but also through social networks or through the pages we visit in our browsers".
"All this started to be stored in huge databases to create risk profiles," he adds. "Now it is not uncommon that when you try to cross a border, you may be asked for your social network passwords."
And the monitoring is not just on the internet. Video surveillance systems were also deployed on a large scale in cities, he added.
"The UK was one of the pioneers of large video surveillance networks in cities," Velez explained, "yet crime has not gone down, even since more modern systems with facial geometry detection or suspicious movement detection have been installed."
However, these systems have been used for repression, Velez flagged, such as in Hong Kong by the Chinese government.
"We thought it before and we still think it today: it is not justified," Frois said. "Security cameras are not able to anticipate crime because there is no surveillance system that is able to read people's minds."
Frois argued that their ultimate purpose, beyond preventing crime, is to convince people that we live in a state of terror. The trade-off for the loss of privacy being a feeling of safety, one that can only be justified by the collective trauma experienced on 9/11, she said.
Is there really a new world post 9/11?
History is shaped by big events that lead to a clear demarcation between the before and after. The attacks on September 11, 2001, offer precisely that but the change was not quite as abrupt as one would think, she added.
"9/11 created a new world order, in the way people understood terrorism in general, and in how certain security and surveillance policies were applied. But these systems had been in place for a long time," Frois said.
"The day they wanted to intercept all communications, it was done overnight. This means that the systems were already in place. The problems of intolerance, racism and xenophobia were already there before 9/11. It turns out that this intolerance was no longer just one-sided, but was taken up by the other side as a struggle, as a de facto war."
The 20th anniversary of the devastating attacks should be one to reflect on what has been won and what has been lost, Velez stressed.
"I think that the latent risk of terrorism, which has sewn itself into the seams of our society, has justified terrifying things such as torture, selective assassinations, military interventions, the consequences of which continue. And I don't think we should forget that September 11 was just one day, but Iraq, Afghanistan and Libya have been experiencing it every day for 20 years," he emphasised.
And in Europe, Velez said, the attacks and subsequent conflicts have led to tens of milions of euros being poured into defence, surveillance systems and weapons, to the detriment of health and education systems.