It's basically a complete lack of trust of outsiders, it doesn't even have to apply to color, background or religion. As an ideology, it has plenty of flaws. But it's not without some merit.

You take care of your own first. That's human nature. But if you take it to the extreme where you assault people for walking down the wrong block (and that happened plenty in the Bronx when I was growing up), then you're part of the problem, not the solution.