One of the reasons for the rise of the far right in Europe, is that it was tabu to talk about problems with immigration. That led people with issues to go to the fringe. In Denmark the centrist parties took away that power from the right, by adopting a stricter stance, making them far less relevant.
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All in all we have been too comfortable for too long. That goes for defense as well. We had assumed problems would go away while cutting defense yearly
They never tried to cooperate within democratic means regarding immigration. they from the start included hate and racism, making their demand unacceptable, thus creating polarization.
https://en.wikipedia.org/wiki/Paradox_of_tolerance