"put enough unemployed people in a ghetto"

That's the problem. They are not put in a ghetto, they choose to create one. It happened in my city as house upon house was bought by immigrant families of the same faith and culture for their offspring or relatives until the indigenous population totally disappeared. The English have done it to other countries as it has been done to them. It seems that's how people prefer to live rather than to be scattered and assimilated. Then the young grow up and claim their area is a no go area for the young of other immigrant or indigenous cultures and you end up with the mess we have in Europe that will surely get worse.
How you stop this polarisation I can't think. Many of my family emigrated many years ago to New Zealand and were told where they had to live for the first few years, and in this way the immigrant population was stopped from forming ghettos.
What the answer is today I don't know, but we have to face the fact that we have a problem that the old ideologies can't address.