London, Madrid, Paris - and now Brussels, Europe's fight against terrorism is set to continue for some time, probably a long time. As world leaders express their condolences and outrage, they also know that there is no quick or easy solution to defeat today's terrorists, especially the fanatics who belong to the Islamic State group, the organization that claimed responsibility for the Brussels attacks.

It is relatively easy to carry out a terrorist attack whether with an automatic rifle, suicide vest or home-made bomb. And no society can provide 100 percent security against such attacks. There are simply too many soft targets, whether train and bus stations, soccer stadiums or shopping malls.

In all of the recent terror attacks in Europe the common element has been disaffected youths of Muslim backgrounds. They appear to have been radicalized partly due to anger at Western interventions in Iraq and Syria, and partly due to their alienation from the mainstream of society.