While "To Brooklyn Bridge" doesn't deal with much of America outside New York City, Crane seems to think that New York could almost represent America as a whole. It's the city of the future, full of excitement and danger, fabulous wealth and abject poverty, modern drudgery and modern fantasy. Hart Crane sees New York as a place of great national promise. The Brooklyn Bridge literally links Manhattan and Brooklyn, but symbolically it stands for the unique melting pot of a city where so many different ethnic and cultural groups live side by side. It New York, even the marginalized "pariahs," including gay people like Crane, could have a voice and a life. No wonder that at the end of the poem Crane wishes he could extend Brooklyn Bridge across the entire country, drawing even more Americans into its orbit.
Crane views modern American life as essentially defined by the urban experience.
The value of the bridge, and of New York, in the poem is that they provide an imaginative space for outcasts and social pariahs.