The moment Wahid Sheikh’s life changed forever was broadcast on television to a global audience of millions, including him. At the time, it appeared to be happening entirely to others, a long way from his Mumbai home. “I watched the buildings collapse, slowly and gradually, sad to watch ordinary people dying,” he recalls.

Vukosava Crnjanski, a Serbian activist travelling in Denmark, remembers crowds huddled around newsagents reading stories hastily printed on A4 sheets. “People looked so intense and tried to explain to me – it’s an attack on the US,” she says.

Ahmed Alaa, in Riyadh, was a child, and does not remember the day at all.

Though separated by distance and different circumstances, in time each would be among those to feel the reverberations of the al-Qaida strikes on the World Trade Center towers and other targets on 11 September 2001.

From Northern Ireland to Tel Aviv, governments had responded to terrorism before by granting extra powers to police and curtailing civil rights. But the US in 2001 was arguably at the peak of its international influence. The attack in New York, perhaps the world’s most recognisable city, was broadcast into homes in every country. The backlash, too, would be globalised.

What followed has been described by a UN human-rights watchdog as an ongoing “security pandemic”. More than 140 countries pushed through counter-terrorism legislation in the months and years after the New York skyscrapers were brought down. Muslim minorities around the world suddenly felt the glare of security services. In some countries, it was political dissidents, environmentalists or anti-corruption campaigners who now found themselves labelled terrorists.

“A lot of these trends pre-dated 9/11,” says Letta Tayler, an associate director with Human Rights Watch, who leads the group’s research on the war on terror. “But we’ve seen an enormous increase in repression in the name of countering terror. Many of these trends are justified as immediate emergency measures – two decades later, they’ve become the new normal.”

The foundations of a new era were being laid by the evening of the attacks. In his address to a traumatised country from the Oval Office, the US president, George W Bush, debuted a doctrine that would come to bear his name. Countries were put on notice to actively pursue terrorists in their midst. “We will make no distinction between the terrorists who committed these acts and those who harbour them,” Bush said.

In late September, meeting only for a few minutes, the UN security council passed the first of what would become several sweeping – and binding – resolutions, ordering member states to do all they could to prevent terrorism or its financing. Sanctions were soon utilised as a threat to any countries that failed to do so.

“It was maybe the biggest power grab in the history of the security council … and it’s still not been reversed,” says Prof Martin Scheinin, appointed in 2005 the first UN special rapporteur for the protection of rights in counter-terrorism.

What was allowed in the pursuit of terror was clear by the beginning of 2002, when Guantánamo Bay was opened as a facility for the US to detain accused terrorists without trial, fed by a system of forced disappearances (relabelled “extraordinary rendition”) and torture (“enhanced interrogation”) that implicated up to 54 countries around the world.

The architects of this new world left something critical undefined. Who, exactly, was a terrorist?

‘What you’re saying is, anything goes’

The police came for Sheikh on 27 September 2001. The same day, India had banned a Muslim students’ group that authorities allege had links to extremists, part of a legal overhaul that would including reviving anti-terror powers that had led to human-rights abuses throughout the 1980s and 1990s.

Sheikh, a school teacher, had orthodox views, but was no extremist and had never been linked to violence, nor to the banned Muslim students’ group, he says. To the officers who subjected him to repeated interrogations over the next years – and, he says, severe torture – his denials did not seem to matter.

“Whenever there was a bomb blast anywhere in India, or any terrorist threat, I would be harassed by the police,” he says.

Muslims made up fewer than 1% of the Maharashtra state police force at the time of the September 11 attacks, according to Josy Joseph, an investigative journalist who profiled Sheikh for a new book on India’s intelligence and law enforcement worlds. Ordered to crack down on Islamist terrorism, Indian police forces already implicated in torture and extra-judicial killings turned their sights on communities where they had few informants and little trust.

When a series of train bombings in Mumbai killed 209 people, police again turned to Sheikh – this time jailing him and a dozen other men over the plot.

During the two years that India’s post-9/11 terrorism law was in place, a parliamentary review committee found at least 11,000 people were improperly charged under the act. Another national-security law, known by its initials UAPA, was widened in 2004 to extend to terrorism. Government data released this year showed the conviction rate under this act, which has led to thousands being held in prison for years awaiting trial, was a little over 2%.

The abuse of power by governments did not start in September 2001, but the war on terror provided repressive states with a new way to brand it, argues Nate Schenkkan, a director at the US-based civil-rights nonprofit, Freedom House. “It gave them a vocabulary,” he says.

Fighting “terrorists” became a globally recognised justification for straying from legal standards, often brutally. “It is a way of saying, this person is outside the law,” Schenkkan says. “When you call someone a terrorist, what you’re saying is, anything goes. I can disappear them, I can kill them, I can hold them without trial for years.”

The al-Qaida strikes did not lead to a single war on terror, he says, but dozens of them, prosecuted by individual countries against their own populations. “There are global wars on terror, and everyone gets to define their own terrorists.”

‘I knew they do this to all activists’

This absence of a shared definition of terrorism has been called the “black hole” at the heart of the global counter-terrorism system built after 9/11. States were quick to grasp the opportunity it presented.

Within a week of the al-Qaida attacks, Chinese foreign ministry spokespeople began to speak of a separatist movement among the country’s Uyghur minority - previously framed as a low-profile internal affair - as part of the global fight against jihadism.

In Chile, members of the indigenous Mapuche tribe who have for decades resisted, sometimes violently, the incursions of logging companies and others on land they consider theirs, had typically been charged with ordinary criminal offences in the 1990s. After 9/11, Chilean governments started used anti-terrorism laws instead.

Alaa’s act of terrorism was to wave a rainbow flag during a 2017 performance in Cairo of the Lebanese band Mashrou’ Leila, whose lead singer is openly gay. He was detained by Egyptian security forces a few days later.

“They kept asking me questions about my whole life – nothing to do with the concert,” Alaa recalls. “They asked about my life, my childhood, my activism, my religious beliefs, and then I asked them: ’Are you going to send me to the doctor to check if I’m gay?’

“The investigator told me: ’That’s not your charge.’”

He was instead charged with offences under Egypt’s sweeping anti-terrorism code, including being a member of banned groups, receiving money from foreign organisations and seeking to change the constitution.

Being labelled a terrorist did not shock him. The military government of Abdel Fatah al-Sisi has one of the worst records of abuse of national security laws against journalists, campaigners, lawyers and critics. “I was an activist, and I knew this happens to all activists,” Alaa says.

A 2019 UN report has argued abuse of terror charges since 2001 is so endemic in every region of the world that it cannot be viewed as an exception – a few bad apples here and there – but rather as “the hard-wiring of misuse” into counter-terrorism systems.

“What we see here is country after country establishing a two-tier system of rights, one for alleged terrorism suspects, and people the government wishes to conveniently label terrorists, and one for the rest,” Tayler says.

Over the past year alone, Saudi women’s rights campaigner Loujain al-Hathloul was sentenced to five years in jail by a counter-terrorism court (she was released on probation in February but is still subject to restrictions), while Belarus forced a commercial flight to land in Minsk, detaining journalist Raman Pratasevich on a terrorism watch list since November. In Tanzania, the main opposition leader, Freeman Mbowe, is currently in prison awaiting trial on terrorism charges.

“When the Egyptian government says we’re fighting terrorism, it’s a green light for their crimes,” says Alaa, who was assisted by a Canadian nonprofit organisation to flee and seek asylum there. “They say, if I’m fighting terrorism, don’t ask me about human rights.”

States such the US and UK occasionally voice careful criticism of Egyptian abuses but continue to give the country military aid and sell it weapons. The French president, Emmanuel Macron, last year awarded Sisi his country’s highest civilian honour. His justification was familiar: a boycott on weapons sales would only “reduce the effectiveness of one our partners in the fight against terrorism”.

‘For the Bin Ladens of the world’

Detentions without trial, torture, extra-judicial killings and other abuses justified by wars on terror are just the tip of the iceberg, argues Scheinin. Below the surface, more wide-reaching and largely unseen, are the electronic surveillance regimes that have mushroomed in many countries over the past two decades.

The attacks on the US occurred just as the internet was accelerating its march into billions of lives. Terrorism has stalked debates over how, and to what extent, this new digital space should be governed.

In rare cases, as in the attempt of the FBI to force Apple to unlock the iPhone of one of the San Bernardino shooters, governments have publicly cited the terror threat to justify breaching privacy. More often, such as in the mass metadata collection carried out by the US National Security Agency – and exposed by Edward Snowden in 2013 – populations have been kept in the dark.

It is likely that states would have sought to bring the internet under control even without the war on terror, but armed with its justification, “the bad things came earlier and faster”, Scheinin says.

Tools initially developed to fight wars on terror have now entered the private market, sold by companies such as Israel’s NSO Group to governments without the ability to do it themselves. NSO has justified the sale of their powerful, invasive phone-hacking software Pegasus as designed for use against “the Bin Ladens of the world”. A former director mused that she had visited the World Trade Center memorial site and wished the spyware had been available then to avert the attacks.

In practice, evidence is now overwhelming that governments such as India, Hungary, the United Arab Emirates and Saudi Arabia systematically use Pegasus to spy on lawyers, journalists and activists. NSO has said it investigates any credible allegations of misuse, but admits it cannot detect human rights abuses unless they are highlighted by the media or whistleblowers.

Rolling back on the world created by the war on terror has proved difficult. In 2016, the Financial Action Task Force (FATF), a Paris-based organisation established by the G7 group to strengthen financial crime laws around the world, reversed a 9/11-era warning it issued that non-profit groups were “particularly vulnerable” to terrorist financing.

That warning had given license for many governments around the world to declare “open season” on NGOs, one analyst told Reuters, freezing accounts and arresting their members on often spurious charges of money laundering or funnelling money to terrorists. It has contributed to suffocating environments for civil societies around the world, of which just 4% are currently considered “open”, according to the watchdog group Civicus.

Yet it continues to be misused by some countries. The Serbian nonprofit, CRTA, monitors democracy in the Balkans – introducing among other things the country’s first political “truth-o-meter”, and its first published parliamentary transcripts.

Last year it was listed along with dozens of other organisations perceived to be critical of the country’s president, Aleksandar Vučić, whose banks may need to cough up sensitive financial information in line with what the government claims is its new global financial standards, passed to comply with FTFA regulations.

Crnjanski fears the information will be leaked to the media as part of a smear campaign to frame her work in the country’s government-friendly media as elitist and unpatriotic. “They want to portray us as people who are getting rich, who drive expensive cars, who are rich foreign agents,” she says.

The Serbian government has not followed through on the order, amid an outcry by FATF and international monitors. But Crnjanski says the damage has already been done: a system empowered to fight terrorism, two decades later, is being misused by rightwing populist governments to crack down on dissent.

“We are trying to develop democracy, to strengthen institutions … It’s about trust in our work, and people are now afraid to approach us. It helps [create] this huge distrust in the work of investigative journalists, in civil society.”

Some of the flood of counter-terrorism laws passed since 2001 may have been necessary and effective. But precisely which laws is unclear, perhaps even to governments themselves.

A Geneva-based research group last year convened a panel of experts, including policymakers, to assess the effectiveness of a range of counter-terrorism measures on the books in several countries. They include the ability to close mosques being used to spread extremist propaganda, bans on “glorifying” terrorism, and police powers to stop and search terrorist suspects.

“There was this idea that there must be a wealth of knowledge here about what works and what doesn’t,” says Michael Moncrieff, a member of the research team that convened the meeting. To their surprise, he says, most governments appeared to have no measurable way to assess if a policy was working – and therefore, if the restrictions those policies imposed on freedoms were worth it.

“The main takeaways were that up to this point, very few governments have really made efforts to monitor the effectiveness of a lot of their policies,” Moncrieff says. “They kind of take it at face value, whether these things are working or not. And even less seen are the side effects upon civil society and areas like that.”

In 2015, Sheikh was freed from from jail in Mumbai after nine years. A long-running terrorism trial found him not guilty, while sentencing five of his co-accused to death. One of them, Kamal Ahmed Ansari, was condemned despite electronic evidence showing he was in Nepal on the day he was accused of planting bombs.

Sheikh has formed a group called the Innocence Network, trying to free those he was jailed with and others imprisoned on spurious terrorism charges. For Ansari, it is too late. Already a victim of one era-defining event, in April he succumbed to another. His family learned through a WhatsApp group that he had become ill in his prison cell and was transferred to hospital, where he died 10 days later. The cause was Covid-19.

• Additional reporting by Milivoje Pantovic in Belgrade