I don't know the exact history, but this reads as something that can't possibly be true. Had the "Irish shantytowns" successfully excluded other minorities? If

I don't know the exact history, but this reads as something that can't possibly be true. Had the "Irish shantytowns" successfully excluded other minorities? If so, how? Is there any "shantytown" anywhere on earth that isn't populated much more densely than 1850s Manhattan? What makes a "shantytown" not resemble a neighborhood? Not enough picket fences?