"Why does the US capitalism, the richest, the most powerful and technological
country in the world, need to base its rule on a primitive ideology as racism? One can understand if that were the case for less developed/ underdeveloped capitalism society."
Don't let the glitz blind you. Just because a country is materially prosperous and industrially advanced doesn't mean that it is bound to use more "sophisticated" or "advanced" methods of repression and class warfare. Racism has worked just fine for two hundred years; so, why mess with a sure thing?
It seems, that in phrasing your question in this way, you're assuming some kind of moral superiority to developed nations over underdeveloped nations; that's kind of like believing that the rich are rich because they're better or more frugal than the poor.
Joanna