What are the reasons for the terrorist attacks in Europe?

Politically, Europe, especially Western Europe and the United States sent troops to Iraq and Afghanistan in the Middle East. Therefore, air organizations have the motive to attack Europe.

In terms of personnel, Europe has a large MSL population, and both France and Britain make them hard to guard against: many of the attackers are British-born. Of course, they are all MSL people. At the same time, the recent influx of refugees into Europe is even more unpredictable.

Finally, security measures. The integration of Europe and the free movement of people between countries is actually a huge loophole. At the same time, European countries regard themselves as representatives of western values and are not allowed to secretly monitor and investigate people, which makes the loopholes even bigger.