A wide, tree-lined street with a large central walk running between Barcelona’s Placa de Catalunya and the Cristopher Columbus statue at Port Vell, La Rambla divides Barcelona’s wonderfully preserved Gothic Quarter from the somewhat seedier El Raval. On summer evenings it is packed with crowds of tourists and those who cater to them, making it a perfect terrorist target.

La Rambla was particularly vulnerable to the type of a low-tech attack by vehicle that has become almost common in Europe. In this attack at least 15 people were killed, with more than 80, including three Australians, injured when a white van ploughed through the evening crowd.

The night before, two explosions ripped apart a house in the town of Alcanar south of Barcelona, killing one and injuring 16. Spanish police have said there could be a connection between the La Rambla attack and the house explosions.

Spain’s last major terrorist incident was in 2004 when 192 people were killed and around 2,000 injured in coordinated bombings of trains in Madrid, two days before the national elections. Spain responded by withdrawing its force of around 1300 troops from Iraq.  

Spanish forces do remain in Afghanistan as part of the larger NATO commitment, although they have a limited, non-combat role there.

Spain has, since 2004, remained relatively immune from the terrorist attacks that have ranged across Europe, primarily due to its low profile in the “war on terrorism”. But La Rambla is constantly packed with people from all over the world, primarily from Europe, America, Canada and Australia, making it a truly international target.

Islamic State has claimed responsibility for the Barcelona attack and it is possible that, as the formal structure of IS crumbles it is seeking to lash out when and as it can. But some of the motivation might lie in the origins of two of the three suspects who were quickly arrested.

One of those arrested, Driss Oukabir, had handed himself in to police saying that his documents had been stolen. Oukabir, originally from Morocco, lives in the Catalan town of Ripoli, about 80 kilometres north of Barcelona.

Oukabir had been imprisoned in Spain, being released in 2012, but had an updated Facebook profile indicating he was relaxed and happy, lying on a beach, posting music videos and showing other reflections of engagement with the lighter side of Western life. Reports say the Facebook profile also shows Oukabir making comments about colonialism and other political views. Police now believe his 18-year-old brother, Moussa, may be involved in the attack.

The other suspect detained was born in the Spanish north African enclave of Melilla. The enclave is a remnant of colonialism in north Africa and, along with the other Spanish enclave of Ceuta, has been a point of contention with many Moroccans and north Africans from the region.

Even though Spain had, until the attack, been terror-free for 13 years, La Rambla was dangerously exposed. Counter-terrorism authorities across the world have been closely monitoring open spaces used by pedestrians following recent vehicle attacks in France, Germany, Sweden and London.

As with Melbourne, bollards and other traffic-stopping devices are now being rolled out in many open areas, in anticipation of such an attack. Such devices might have diminished some of La Rambla’s easy charm and perhaps congested some of the already packed crowds found there. They will now almost certainly be put in place, if after the event.

The problem with such defences against terrorist attacks is that, as with the use of vehicles, terrorists have shown themselves to be remarkably adaptive. As one barrier is put in place, terrorists simply find another method of attack.

There is no complete answer to this almost random terrorism. The gradual destruction of Islamic State in Iraq and Syria has been important, but only reduced that organisation’s conventional war-fighting capacity.

Many of IS’ more hardened fighters had left before the fall of Mosul and are reported to have also left Raqqa, which is under siege. Critically, too, while international focus has been on Islamic State, Al Qaeda has been rebuilding, in Pakistan, Yemen and in the Maghreb — the north-western corner of Africa.

The names might change, along with the origin of the actors on the jihadist stage, but militant Salafi ideology is far from diminished, much less defeated. And they are not just a recent phenomenon, so cannot be expected to disappear any time soon.

In the past the types of conflicts that generated jihadists were much more localised. But that was then.

In the West, all open spaces must now be considered as vulnerable to potential attack. Whatever its motives and origins, in a globalised world, having the “war” brought home is now an inescapable fact.