

In the early 90s something similar happened in Belgium (1).
What lessened the extremism in the following couple of elections was investment (in infrastructure, healthcare, economic opportunities, etc) outside of the cities as well.
It turned out that for every tax frank gathered, 80 cents were spend on prettifying the larger cities and the major port. People were mostly (rightly?) pissed off that government represented a terrible ROI for the same group of people for decades. They would’ve been better of without a federal government. They saw their lives get worse, whilst at the same time that government applauded themselves for the great things they achieved.
I’m not sure how feasible the same solution is today, as there’s very little investment budget anyways. Most of tax revenue goes to pensions and healthcare of a reversed population pyramid.
I wonder if they can, with the reversed population pyramid most EU countries experience.