"People think that there's al-Baghdadi sitting in Raqqa or Mosul and providing directions to all these cells across the world in this very hierarchical structure, and that's just not how it works," Christian Leuprecht, professor of political science at the Royal Military College of Canada, senior fellow at the Macdonald Laurier Institute, told Radio Sputnik.
"These attacks are more Daesh-inspired, so they are inspired by ideological extremist and that's what makes it so difficult to mitigate or prevent these attacks because there's a significant minority of people who are drawn to the violent extremist ideology that Daesh diffuses, but very few of those people actually move from thought to action."
"The challenge that security forces have is trying to ascertain the individuals who are likely at risk of moving from thought to action," and they need to better coordinate their intelligence both within and between states.
"After the Charlie Hebdo attacks one French intelligence official said that they were concerned about some 6,000 people in France, and there are simply not enough security personnel to watch all these individuals."
The ease of spreading violent ideology using the internet and electronic communication means that terrorist sympathizers can be found everywhere in the world, and all countries face an inherent risk of terrorist attack.
"Nobody really can say that they or safe or immune from either the ideology or the possible repercussions of people moving from thought to action and so there is some merit in the Europol statement that it is not a matter of if but when we are likely to see more Daesh-inspired attacks."
However, some countries like France and Belgium seem more vulnerable than others to the risk of their citizens traveling to the Middle East and returning with the expertise and desire to commit terrorist attacks. Though Belgium has about one eighth the population of Germany, a similar number of people have traveled to Syria from both countries, Leuprecht said.
Large-scale attacks like those in Jakarta in Paris often have involvement from people who have traveled to the Middle East and networked with terrorists and gained training there, for example in surveillance, the building of suicide vests or how to procure and use weapons.
"The other problem is that among returnees it is very difficult to prosecute or has been difficult to prosecute 'veterans' once they return because much of the evidence that we have is intelligence evidence that will not be admissible or stand up in a court of law."
"Of course not all veterans return to commit acts of violence, nine of ten actually return with serious mental health issues, it's not clear whether they had those mental health issues before they went or they got these mental health issues as a result of going. But we also know that one in ten tends to return as a hardened ideologue and often quite committed to engaging in criminal activity."
These problems are compounded by the inability of agencies within and between countries to share information effectively, sometimes because of a lack of trust.
Leuprecht gave the example of the failure of the FBI to listen to Russian authorities in 2011, when they warned the agency to detain Tamerlan Tsarnaev, one of the brothers who carried out the Boston Marathon bombings in 2013.