Then what is the correct word for the set of behaviors, attitudes, arts and beliefs that are demonstrated by the american mainstream and distributed to the rest of the world? I've always used the word culture to describe that, but is there another one?

Or are you saying that the heterogeneity of the population of the US means there's no single culture? If so, then you must realize that people say "US Culture" what they really mean is "mainstream culture" I.E. Mcdonalds, Britney Spears, The Simpsons. What do you call those things if not cultural fixtures?