One thing about long distance driving is that it reminds you of just how big this country is. It's a revelation to anyone who's done it - and it's easy to not do it in this day of Jet airliners. A century ago in Dvořák's day, long distance travel was by train and there was no getting around the vastness of the land.
The Philadelphis Philharmonic Symphony commissioned Dvořák to write this piece. He said that he was influenced by Native American and African American music, especially in this, the second (Largo) movement.
As for me, I've never picked up on American themes, although some of those from his native Bohemia seem to sneak in. Still, it's a nice sentiment.
This is by far Dvořák's most famous piece, although this may be more familiar to most people.