They just did it.
There's an even simpler explanation: The Germans came. Then the Poles. Then the Italians. Then the Chinese. Those dirty immigrants? They may be taking your job but your kids are also playing with their kids. Then they're going to grow up and bitch about someone else taking their jobs.
All immigrants must be treated like absolute dogshit for one generation. Those are the rules worldwide. Kids born there get to be pissy about how their parents were mistreated but are generally orders of magnitude better off. Their kids? Those are full-fledged citizens. The trick is in who chooses your identity - yourself or the neighborhood. if you get to identify as a Chinese-American, you win. If your neighborhood identifies you as Chinese in America you lose.
Blacks are fucked under this system because few of them chose to immigrate, therefore their second-class status has been semi-perpetual. This is one reason why modern blacks favor better in the Commonwealth, although it isn't all wine and roses. Jews also fare poorly because they integrate less than other ethnic groups.