There was no shortage of labor after WW 1 or 2 despite the millions killed and vast amount of reconstruction needed. Industry was mostly destroyed, and there weren't all that many jobs. Govts' encouraged women to "return to hearth & home" - give up their jobs to make way for men to be hired. The problem was Algeria - soon-to-be-former French colony - and an influx of Algerians, and those posing as Algerians.
By the 1980s-90s, France was not stringently enforcing its borders, especially the Mediterranean & port of Marseilles. Overpopulation in Africa, largely unskilled & useless, could get into France. And the flood turned into an invasion throughout Europe.