The strategy is blatantly clear, the extremists knew that the attack would create an immediate and powerful backlash towards all refugees and muslim immigrants. They want that backlash to be felt by young, impressionable muslims. They want them to feel persecuted and racially/religiously discriminated against, so much so that they become radical. Creating that tension ensures recruits. They actually hope for the most severe responses possible because they believe, in the long run, it will just create more hatred for the west among the population.
There is no simple solution to this. It's kind of a damned if you do, damned if you don't situation. And, before anyone says the simple solution is to nuke the middle east because it worked for Japan, that's not a comparable situation. Japan had a very structured, organized government and the country was a relatively small target. Radical islam is an ideal, not a structured government located on a small island nation. It's spread everywhere. You can't nuke an ideal, blowing everything up in one middle east country isn't going to stop radical islamic ideals everywhere else. Indiscriminate slaughter is only going to embolden their movement.
