One takeaway from that incident was the notable resilience and dignity in the response of London and its people to the attacks. This led to important thinking, within government and in policy-oriented academia, about "bouncebackability". We may not have the sangfroid of the Londoners, but we have at least begun the journey.

As a society, Singapore has always emphasised the need to build trust between communities and decades of work have gone into developing such relations. The Inter-Racial Confidence Circles (IRCCs), set up in 2002, helped entrench these efforts, as did the Community Engagement Programme, launched in 2006, with the latter now receiving an important refresh through the SGSecure movement.

For every visible success story, there are those that exist, equally successfully, just below the radar.

This has included efforts to engage the Malay/Muslim community through behind-the- scenes dialogue, which has been crucial in ensuring the JI arrests did not fray communal relations.

Also critical have been the efforts by the Religious Rehabilitation Group (RRG) working with detainees, in turn complemented by the work done by the Inter-Agency Aftercare Group, which assists the families of detainees.

Over time, all these efforts when put together are coming together to assume the form of a national movement.

SOCIAL MEDIA AND IDENTITY POLITICS

While efforts went into confidence building and shoring up resilience, the spread of Islamic terrorist ideology to multiple groups across the world via online communities was not something many security agencies could have foreseen.

The JI was responsible in the last decade for a litany of terror acts - Bali in 2002 and 2005, and Jakarta in 2009. JI and its splinter groups remain a threat notwithstanding the fact that its leadership ranks (Hambali, Abu Dujana, as well as its spiritual leader Abu Bakar Bashir) have been decimated through arrests and its most skilful operatives killed (Noordin Top, Azahari Husin).

In 2001, however, one could not have known what the sheer scale of the problem would turn out to be and the sheer multiplicity of threats that would develop, quite apart from the JI.

Security practitioners and academics failed, until later on, to appreciate the full radicalising force of social media. It is no accident that home-grown terrorism began to enter security lexicon at the same time social media really began to take off - around the middle of the last decade.

Social media has not in the end turned out to be the greater denominator for some communion of humanity. Instead, it has cocooned us within echo chambers of reinforcing, and in many cases intolerant, identity.

As Foreign Minister Vivian Balakrishnan commented in April this year at the Asia-Pacific Conference for Senior National Security Officers: "We now live in a world where no matter how crazy you are, you can find someone crazier than you to affirm your views on the Internet. So it should not surprise us that in fact it has led to a sharpening of radicalism, a sharpening of exclusive identities and a reaffirmation of the temptation to resort to violence, both physical violence or even political violence, as people search, emphasise and reaffirm identities, imagined or real."

The JI, though extant, is diminished. So too is the Islamic State in Iraq and Syria (ISIS), fighting for the territory of its caliphate in Syria and Iraq. Some experts posit that ISIS' cruelty and wanton violence have sown the seeds of its own eventual rejection.

This is a simplistic view. Intolerance, with new media as its rocket fuel, is in fact the real legacy and afterlife of ISIS.

TERRORISM AS HATE CRIME

Terrorism as hate crime shows signs of becoming commonplace.

Like the murder in March this year of an Ahmadi shopkeeper in Glasgow, Mr Asad Shah, known for wishing his customers Happy Easter. His murderer, Tanveer Ahmad, travelled over 300km from Bradford to confront and kill him.

Like Ms Ibolya Ryan, an American kindergarten teacher, stabbed to death in December 2014 in the women's restroom of an Abu Dhabi mall by an Emirati woman, Alaa Badr Abdullah al-Hashemi (who had been looking for a random foreigner to kill), while Ms Ryan's young twin sons waited outside for her.

In both cases, the killers were not card-carrying ISIS members. In both cases, social media had played a part in their mental journey.

Intolerance is the new radicalisation, abetting senseless acts of violence within the routine fabric of our lives. This is what we have to be prepared for.

Many of the future perpetrators of so-called terror acts will inhabit virtual worlds where everyone reinforces one another. There will be no need in these worlds to force one to reconcile to someone else's opinion. Therefore, when going head on against someone else's differing perception of issues, it is all the more easy for the disagreeing party to be easily branded a deviationist.

This is identity politics at work and should not solely be seen as a problem with Islamist extremism. There are many galvanising creeds apart from Islamist terror - white nationalists, for example. What will come next ? Anarchists? Individuals drawn to the conflict in Rakhine state, attempting to help their co-religionists - potentially even on both sides, Muslim and Buddhist, of the conflict?

The inescapable fact is that we live in a future where people will be fighting for all sorts of causes, fervour fuelled by online messages into furious action.

THE THREAT IN THE REGION

The South-east Asian region will turn out to be an insalubrious place for a second reason. The number of South-east Asians who fought the Soviets in Afghanistan was probably never more than a thousand.

In the last three years, it is likely that more than that number of South-east Asians have made the trip to join ISIS. Some are beginning to return here. Nor is it just natives from the region - Indonesian and Malaysian fighters and perhaps the few Singaporeans thought to be fighting for ISIS - who will make the journey here.

Already, several plots and cells that have been interdicted in the region have featured foreigners from outside the region - Uighurs, in particular, and the odd Moroccan here and there.

The region might thus become a miasmic arena where drifter radicals, unable to go home to the West for various reasons, chance their luck here.

They will hope to make common cause with issues such as the Rohingya. They will also seek to leverage on the febrile mood in the region - religious practice formerly inclusive and syncretistic becoming intolerant, increasingly fed by governments seeking to burnish Islamist credentials.

ISIS' loss of its caliphate is not the end, but perhaps the end of the beginning.

Fifteen years after 9/11, we still do not fully understand what radicalises someone - this is a failure not simply on the part of security services, but also the increasing numbers of academics and psychologists who have turned their minds to the issue.

In some cases, we can make good guesses. One can understand the motivations of a young angry man from the French banlieue with no prospects and with a police record who becomes an ISIS aspirant.

But many radicalised individuals were integrated in their societies, with good jobs and prospects. Understanding their trajectory is not so simple.

Nor do we fully understand why some who go through counselling or deradicalisation become recidivists. This has happened, at least twice, in Singapore.

SGSecure has an app, but there is no app to detect or predict radicalisation or recidivisim. What risk assessment tools that do exist, largely adapted from the study of violent offenders, are by and large imperfect.

What we do know, however, and what senior officials from the security establishment have repeatedly said, is that "you can't arrest your way out of the situation".

We should not shy away from borrowing the best of Countering Violent Extremism (CVE) practices from countries in the West. Some nations have decided that it is vital to go very far upstream in the CVE stakes.

They are trialling pilots in critical thinking skills in schools - when confronted by ISIS propaganda and recruitment matter, youth are being schooled in the ability to rationally interrogate the source material.

In other countries, there have been attempts in diversion (through seed money for sporting or cultural activities, for example), in terms of deflecting the trajectory of people who might become at risk down the line.

This kind of resilience is important. For their part, policymakers worldwide will need to accept that these embryonic methods do not lend themselves to a straightforward cost-benefit analysis or control groups.

But the stakes are too high not to try.

• Dr Shashi Jayakumar is head of the Centre of Excellence for National Security at the S. Rajaratnam School of International Studies, Nanyang Technological University.