Terrorism is effective because it always seems near. It always seems new. And it always seems personal. Ever since the first wave of terrorist violence broke across the newly industrialised cities of the west in the late 19th century this has been true.

It feels personal because, although statistics may show we are many times more likely to die in a banal domestic accident, we instinctively conclude from an attack on the other side of the street, the city or, in the case of New Zealand, the other side of the world, we might be next.

Terrorism always seems near – at least when it happens in an environment resembling our own – because the shocking images on our phones, televisions or newspapers erase the distance between us and the source of danger. It always seems new because although each attack follows a familiar timeline – the first reports amid chaos and confusion, statements by police and politicians, analysis from commentators waking up in successive time zones, the identification of attackers and victims, condolences and flags at half-mast, debates about radicalisation etc – each is unique. In the 1970s, terrorism expert Brian Michael Jenkins famously said that “terrorism was theatre”. This succinctly captured its spectacular, performative nature. These days, it seems more like an endless TV series that everyone wishes was over but that everyone watches nonetheless.

That Brenton Tarrant, the 28-year-old Australian who shot dead 49 worshippers at two mosques in Christchurch, broadcast the attack live on Facebook via a helmet-mounted GoPro camera is a new low, but a logical and sadly inevitable one.

Most people naturally assume that the technological changes that influence terrorism are those involving weapons or explosives. But the big shifts in this field happened long ago. Dynamite was patented in 1867 and automatic weapons became widespread after the Second World War. If terrorists have made the occasional use of chemical weapons or a hijacked plane, the vast proportion of modern-day attacks use technology that, in its essentials, is not new. What has changed beyond recognition are the media that enable individuals or groups to disseminate their message.

On 11 September 2001, Osama bin Laden knew no one could stop live images reaching a billion people in the Islamic world. Photograph: Allsport UK/Allsport

The significance of this is often missed because we are too focused on the violence. Terrorism is “propaganda by deed”, the term coined in the 19th century by its first modern practitioners. Violence alone is not enough. That violence has to terrorise – inspire irrational fear and so change minds – but has to radicalise and mobilise too. It has to send a message to enemies, supporters and, perhaps most importantly, those who are neither. Al-Qaida and Isis made this explicit. So did Tarrant’s “manifesto”. Every change in media technology over the past half century or more, arguably much longer, has made it easier for terrorists to achieve this aim. In the 1950s and 60s, radio and the new photojournalism meant violence could influence public opinion thousands of miles away in colonial powers. So extremists chose terror tactics in the last days of the British mandate in Palestine and during the Algerian war of independence against France.

In the 1970s, terrorists were quick to grasp the potential of overseas TV broadcasts. The terrorist attack on Israeli athletes at the Munich Olympics in 1972 was covered live by the world’s networks. The operation had been designed to exploit this new capacity. In the 1990s, it was the advent of satellite TV. No longer did western editors or those working for Arab regimes control what news went out to the masses of the Middle East. The channels of communication were becoming more direct and that was hugely empowering for the militants. On 11 September 2001, Osama bin Laden knew no one could stop live images of his group’s massive attacks in the US reaching the billion people in the Islamic world who were his primary audience.

Then came the biggest change: digital. As media organisations evolved, so did terrorist ones. Top down was out, peer to peer was in. There were citizen journalists who followed broad guidelines but were not formally affiliated to an organisation and “freelance” terrorists who did much the same. The mainstream media were increasingly redundant. Why fight to get on the BBC or al-Jazeera if you could just create your own channels and reach your audience directly? Isis showed how effective that could be.

‘The terrorist attack on Israeli athletes at the Munich Olympics in 1972 was covered live by the world’s networks.’ Photograph: Associated Press

Rightwing extremists were slower to exploit the potential of this seismic shift. Now, with the Christchurch attack, they have caught up. There have been live streams of terror attacks before – a French extremist streamed on Facebook the knife murder of a policeman and his partner in 2016 – but none as high profile.

It is often said we get the media we deserve but that is a simplification. But the media, like terrorism, are part of our societies and, like terrorism, are influenced by broader trends. Perhaps the most striking element of the atrocity in New Zealand is how the filming of the video was an integral part. “Let’s get this party started,” Tarrant says, as he gets into his car, talking directly to the viewer. He shoots images of his face in a twisted version of that most contemporary of phenomena: the selfie. The point of the attack is not just to kill Muslims, but to make a video of someone killing Muslims.

Tarrant said in his “manifesto” that he did not seek to die, but accepted that might happen. But he will still be seen as a martyr to the cause by supporters. The word martyr is of Greek origin and refers to a witness. The Arabic equivalent has similar roots. Witnesses need an audience or their acts are empty. For some terrorists, that witness is God alone, but these are few. For a growing number, that audience, via Facebook, via virtually unmoderated sites in the dark corners of the web, via the mainstream media they so detest and suspect, is everyone.

In Tarrant’s world, on his live stream, in his own mind and those of his followers, he is a warrior, a racial hero, a leader but also, in a wider contemporary sense, a celebrity, if only for a moment. In a terrible, twisted way, he is not wrong.

• Jason Burke’s latest book is The New Threat

• Crisis support services can be reached 24 hours a day. In New Zealand, the crisis support service Lifeline can be reached on 0800 543 354. In Australia, Lifeline is 13 11 14. In the UK and Irish Republic, contact Samaritans on 116 123. In the US, the National Suicide Prevention Lifeline is 1-800-273-8255. Other international helplines can be found at www.befrienders.org.