It is the result of soft immigration policies. The Immigration situation in this country allows foreigners to enter, to live in isolated communities with others like themselves, to learn just the barest smidgen of our language, and to continue on in their virtual native culture. So, this garbage about their being homegrown and radicalized here is a serious error. They are not assimilating into our culture if they are living in isolated Islands of their prior culture and being radicalized in them.
Immigration without assimilation is colonization.