O you youths, Western youths, So impatient, full of action, full of manly pride and friendship, Plain I see you Western youths, see you tramping with the foremost, (9-11)
These Western men are full of action, sure; we saw that coming. But friendship? Of course, it's "manly" friendship, but still. These lines clue us in to the fact that the bond of love and friendship is one of the most significant attributes of these pioneers. It is what unites them.
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, (33-35)
This image of clasped hands is an image of friendship and solidarity. Despite the fact that they are all very different people from very different places, these pioneers are like blood brothers—after all, they share the same "continental blood." And we all know that being blood brothers is like the highest level of friendship.
On and on the compact ranks, With accessions ever waiting, with the places of the dead quickly fill'd, Through the battle, through defeat, moving yet and never stopping, (49-51)
That detail of the compact ranks demonstrates the closeness of these pioneers. They share the bond of soldiers in battle—they're foxhole buddies. This recurring image of the pioneers as an army in formation is central to this poem and really drives home the importance of their bonds of loyalty and friendship.