But just a few thoughts - there`re some European states who are "jeopardized" by terrorism, and another ones that don`t have that problem. Why?

I`ll give you an example in former Yugoslavia - there`re some Croatian dissidents political groups in Western Europe. They published various books and text against communism, and for independent Croatia. There`re some radical terrorists organizations, too - from bombs to plane hijaks and armed groups...
After the independency,1991., there`re now known that most of that radical groups are leaded by YU secret agents, or they have some UDBA (secret police) agents provocateurs inside. Every stupid bomb action was a great political minus for their actual political goals. And nice excuse for political and police terror between intelectuals inside the Yugoslavia. And like "ace" in the sleeve in foreign politics. If UDBA didn`t control or discredit some important political emmigrants, then they just killed them - tens of those murders, mostly in Germany. These days, Muenchen court opened one old case, where UDBA agents killed former director Durekovic of leading petrol YU company (INA), who emmigrated in Germany and wrote the books about corrupted communist goverment. The court proved that many "respected" Croatian (former YU) politicians/policemans were probably secret agents, responsible for very suspicious things in Germany.
And you know what? Even new Croatian goverment obstructed the trial, they didn`t give some very important documents/dossiers.
Who trained those groups, give the money and arms, who are the agents between them and why...who were the UDBA agents/cooperators in YU, anyway?
Even today, the truth cannot be known to the "ordinary people".
Have no time and will to go in details, but you can have a part of the picture.

Not the same situation that we have now, but just the illustration that terrorism problem can be more complex than we can even dream about.
And today`s (Islamic) terrorism problem can be solved in a week - by fair political solution for all sides (Israel and Palestinians, etc.).