Yes, and what could be that something special?
Imperialism says you? Britain and France have been struck by terrorism yet they no longer have an empire. Ok, guilt by association could be a motive... But then why would Belgium and Germany be struck? oh, and Sweden too? And all these kidnapped christian girls in Nigeria? and in every case by Sunni-Muslim...
Maybe it's anti-imperialism, who knows... perhaps some middle eastern sunni muslims were really upset that Sweden ever had an empire, and decided that ramming a crowd with a truck was a good way to avenge the "oppression" perpetrated by Sweden 300 years ago.
That, or maybe you could adjust your worldview, and realise that religious fanatism has been a pretty strong motivator for atrocities throughout history, and even in such enlightened times as ours, there are still people who would conduct the most horrendous acts for their faith and the credibility it gives them within their group.
In all cases, the Chinese, who also suffered from such attacks (the perpetrators were of the same religion), found a "solution" that is much more aligned with imperialistic norms throughout history. They have not been struck since.
And no, be at rest, I am not for the establishment of a surveillance state, but pointing the wilful blindness in your reasoning.