It shouldn't have been just unemployment since that affected more than just descendants of immigrants. If it was the ostracisation, how did that come about? Or were other factors in play?"
The 3rd generation arrived at the wrong time, unemployment, failure to integrate in France, but being foreigner in their grandparents country, being ostrazied for employment and in daily life, many ended up hating "La République".
A perfect breeding ground for the Islamist recruiters, financed by some MEA countries. Or for drug importers looking for foot soldiers.
France's successive governments being completely blind and at lost how to react except by harsh police repression.
Oh, and you can't kick them out as they are French, and not even bi-national anymore. They need a visa to visit their grandparents country !"