From Nebraska, from Arkansas, Central inland race are we, from Missouri, with the continental blood intervein'd, All the hands of comrades clasping, all the Southern, all the Northern, Pioneers! O pioneers!
Okay, maybe he doesn't just like Colorado. He seems down for the Great Plains and a few other regions, too.
He's celebrating different parts of America by naming and listing a few.
He's also celebrating the bond that connects them—that clasping of hands. He calls them "comrades" and suggests that they all share the same blood and veins.
That "intervein'd" is a really interesting word; we can see the image of these veins crisscrossing the country, interconnecting the states and the people that occupy them. Wait, he's not referring to the Interstate Highway System is he?
There's a definite sense of a unity that connects all that diversity. No matter how different these folks are, according to our speaker, they're all joined through one thing.
What's that one thing?
O resistless restless race! O beloved race in all! O my breast aches with tender love for all! O I mourn and yet exult, I am rapt with love for all, Pioneers! O pioneers!
O! O! O! Our speaker is getting really excited.
Now, he just about overflows with his love and admiration for this pioneer race he's been talking about. His breast aches for them! And no, he's not talking about his actual chest. Nope, he's using metonymy to refer to his heart or his soul, which is closely associated with his breast.
We can't help but notice the delightful sounds in the first line. Our speaker can't resist this restless race. Turns out Walt has a bit of a knack for alliteration, or repeated consonant sounds.
That restlessness makes them keep moving, keep pioneering, so it makes sense that our speaker admires restlessness, given how much he loves pioneering.
But why does he mourn? That seems odd.
It seems like another reminder of the perils that pioneers face.
But the mourning definitely doesn't overwhelm the tender and rapt love that he feels. He mourns "and yet exult[s]."
And, to be fair, if you're always pioneering, you're always leaving places and people behind. That can get pretty sad after a while.