The French didn’t grant automatic citizenship to natives of former colonies after decolonization. The British did sort of, they granted the right to British passport to natives. The French didn’t and certainly didn’t to the Algerians after the bitter war they fought for independence.
The immigration from North Africa has been a result of the need for workers; they’ve allowed them in to work on work permits. Then of course, it all spun out of control.
Birth control and abortion have unintended consequences.