The US is unique among Western Hemisphere countries in that, until very recently, intermarriage among the "races" has been very uncommon. By contrast, intermarriage has been so common in Mexico, Central America, and South America that racial distinctions have largely disappeared.

As Warren Beatty said in Bulworth:

All we need is a voluntary, free-spirited, open-ended program of procreative racial deconstruction. Everybody just gotta keep fuckin' everybody 'til they're all the same color.