The atrocities in Barcelona and Cambrils are the latest examples of this.
The continent’s police and security agencies have long known that the demise of the so-called Islamic State would signal an increase in the tempo of attacks, and definitely not an end to the threat of Islamist extremists.
Three attacks in the UK in as many months were the first indication of the nightmare scenario they feared; that the leaders of this rapidly disintegrating so-called caliphate would compel their footsoldiers to launch attacks across the West.
After all, the model for this kind of scenario played out more than a decade ago, when the most feared terror group at that time, al Qaeda, felt the full wrath of coalition airstrikes and ground operations.
Al Qaeda’s leaders urged their followers to strike back – and they duly did, launching attacks in London in 2005 and here in Spain in the capital, Madrid, a year earlier.
For the security services, the complicating factor this time around is not just that IS has fully trained killing machines who have trodden the battlefields of Syria and Iraq.
The terror group has an even larger army of “sleeper” extremists in towns and cities across the European continent and beyond.
Most of these radicalised individuals – 3,500 in the UK alone – have never even been to the Middle East. They learned their deadly craft online.
And increasingly they have turned to a less sophisticated, but just as deadly, mode of attack.
What do we mean by less sophisticated? Vehicles and knives. Essentially everyday items that were never meant to murder or maim.
Security sources have told me that they face a two-pronged threat.
Alongside those battle-hardened jihadis are the violent wannabe jihadis who lack the skills, but are just as determined to inflict their brand of misery – often on their own communities.
Authorities here in Spain and elsewhere in Europe have noticed an alarming increase in the number of those who seem to choose the path of violence.
Most of these plots get disrupted before they have a chance to kill and injure innocent civilians, but sadly some slip through the net.
The unfortunate truth here, is that a net increase in plots will result in a net increase in successful attacks.