A series of attacks in Europe over the summer months has raised the number of people killed in the West by jihadists during the past three years to more than 420, writes Dr Lorenzo Vidino.
The deaths of 16 people in Barcelona and Cambrils earlier this month highlighted the continued threat posed by Islamist militants.
The first look at the data behind the attacks – everything from the age of the perpetrators, to immigration status – offers an insight into those responsible and how they might be tackled.
Where the attacks were
We identified 63 attacks between September 2014 and late August 2017 that we considered to be acts of jihadist terrorism.
A relatively limited number of countries were affected: nine in Europe – those named above, plus Denmark and Sweden – along with the US and Canada.
Regardless of country, most attacks were in large towns and cities – including Barcelona, London, Manchester, Paris, Nice, Berlin, Brussels, Stockholm and Orlando.
We looked at attacks motivated by jihadist ideology, that involved deliberate acts of violence against other people and were intended to intimidate or convey a message to a larger group. Other organisations use different definitions.
Researchers used open-source material and interviews with officials
It is possible that some attacks did not come to our attention, or that full details are not available
The research covers the US, Canada and the 28 member states of the EU, plus Norway and Switzerland
Attacks motivated by other ideologies – such as the murder of Jo Cox – are not included in this study
The dead and injured
In total, the 63 attacks caused 424 deaths and left almost 1,800 people injured.
The perpetrators are not included in these figures.
In the UK, Khalid Masood, was 52 when he drove into pedestrians on Westminster Bridge and stabbed to death a police officer at the Houses of Parliament.
The relationship between terrorism and migration is a complex one and has been at the centre of extremely polarising debates, particularly during the European migrant crisis.
However, the number of attackers who were illegally in a country or who arrived as refugees is small.
Two-thirds were citizens of the country they attacked, with others either legal residents, or legal visitors from neighbouring countries.
However, individuals who were in the West illegally also carried out deadly attacks.
At least two of those involved in the November 2015 Paris attacks are thought to have posed as refugees to enter Europe through Greece.
Three other individuals were refugees or asylum seekers at the time of attack, while seven were in the country illegally or awaiting deportation.
The latter group includes Uzbek national Rakhmat Akilov, who killed four people with a hijacked lorry in Stockholm in April 2017, and Tunisian citizen Anis Amri, who also used a lorry to commit his attack at the Berlin Christmas market.
There is also one case of “terrorist tourism”, involving Egyptian citizen Abdullah Hamamy, who lived in the United Arab Emirates and attacked soldiers at the Louvre in February 2017.
They were also executed in part by former foreign fighters.
However, the two other most deadly attacks – those in Orlando in June 2016 and in Nice in July 2016 – were carried out independently by individuals without operational connection to a jihadist group.
These episodes demonstrate that terrorist sympathisers who never travelled to conflict areas and who act independently can be as dangerous as a team of highly trained militants.
Overall, links between attackers and jihadist groups operating overseas are not always easy to determine.
Of the attacks that have hit the West since June 2014, fewer than one in 10 was carried out under direct orders from the leadership of IS.
In some cases it can be difficult to tell, for example IS said it was behind both the Las Ramblas and Cambrils attacks, but it did not provide any evidence.
Nevertheless, the influence of IS can be clearly seen.
During or before the attack, six out of 10 perpetrators pledged allegiance to a jihadist group, almost always IS – which frequently claims responsibility.
Learning the lessons
Unsurprisingly, given the frequency of attacks and the number of deaths and injuries, jihadist terrorism has come to the fore of political debates in the West and receives widespread news coverage.
The threat is not expected to wane in the near future, with policymakers, counter-terrorism officials and the public all being asked to take action.
There are huge implications for domestic and foreign policy throughout Western countries.
It is hoped that knowing more about the attacks and the people who carried them out will help us all have a more informed debate about what action is needed.
About this piece
This analysis piece was commissioned by the BBC from an expert working for an outside organisation.
An earlier version of this piece was published on 14 June 2017. This version provides updated figures, based on the attacks that have subsequently taken place.
