According to our speaker, pioneering is a lot like battle. Conquering new lands, setting up shop in new territories, all thanks to some brute strength and serious perseverance. And never ending ranks, too.
Lines 2-3: Weapons? Pistols? Axes? Sounds like a major turf war to Shmoop. Why do you need weapons to pioneer? This is the first hint that much of the poem will be devoted to an extended metaphor that compares pioneering to waging war.
Line 19: These pioneers are seizing world through hard labor and marching. That sounds a lot like an invading army to Shmoop.
Lines 21-23: Here, the speaker straight up says that these guys are conquering.
Lines 41-43: In this stanza, the speaker evokes the American flag, and sounds suspiciously like he's issuing a patriotic battle cry, asking these pioneers to do their American duty and push west. By calling the flag a "mistress," he personifies it.
Lines 49-51: These compact ranks will never run out of soldiers to fill them, because every time one pioneer dies, another will hustle up to take his place. No matter what happens—even total defeat—they'll keep pushing west. That, friends, is determination.
Lines 53-55: Here, the speaker suggests that it's fitting to die in the name of pioneering. That sounds an awful lot like a military general, telling his soldiers, dulce et decorum est pro patria mori.
Lines 81-83: Hey, even the ladies get in on the battle action. Here they're called to move in united ranks, too.