The USA - constitutionally - is a single nation. Operationally it is a collection of cultures.
Our perception of the USA tends to be influenced by the media representations we see - usually of the oceanic states. On the Atlantic side we see the centre of federal government, a world city and some of he most respected universities in the world. On the Pacific side there is the most important entertainment production area in the world and cities like Seattle. In between there are important manufacturing and commercial cities.
But there are also places which, culturally, belong to the third world.