Whitman starts by taking off. Before we know where he is headed, the speaker is already airborne, "I fly like a bird", and the simile sets the terms for everything after it. This is a view from above, where borders shrink and a continent can be taken in at a glance. Yet the bird does not fly in a straight line. It goes "around and around to soar," a looping motion that suits the poem's real ambition: "to sing the idea of all."
The poem is less a description than a promise. The speaker announces a tour of the nation in song, setting out from Paumanok, Whitman's name for Long Island, where he was born. He heads north for "arctic songs," then through Canada and the Great Lakes states. After that he moves down through Ohio, Indiana and Missouri, across the South, and finally "up toward California." Nothing has been sung yet. The poem ends just as the singing is about to begin, so what we read is an intention, a poet clearing his throat on a very large stage.
The central idea is unity that does not erase difference. Whitman wants to sing first "the idea of all—of the western world, one and inseparable," and only "then" "the song of each member of These States." Each place keeps its own voice: the songs of Wisconsin, Iowa and Minnesota are "inimitable," a word tucked into parentheses like a quiet murmur of admiration. The capital letters in "These States" make the plural feel almost physical, as if he were pointing at them one by one while insisting they are also a single body.
A tension runs through the poem, and it is typically Whitman. The speaker keeps promising to sing "theirs", and the repeated pronoun makes him sound like a generous visitor who gives each region its own turn. But he also says he will travel "till I absorb Kanada in myself." Listening and swallowing are different things. The "I" here is both a guest and a vacuum cleaner, taking in whole territories so it can speak for them. The phrase "to roam accepted everywhere" shows what he hopes for in return, a welcome in every place.
The construction carries this ambition. There is no rhyme and no regular meter. Instead the poem is held together by repetition. Line after line begins with "To," followed by a place name and the refrain-like "to sing," so the effect is of a traveller ticking off stops. The place names do the work that rhyme would do elsewhere. "Wisconsin, Iowa, Minnesota" and "Tennessee and Kentucky" have a rolling, drumbeat sound, and the poem trusts that the country's own names are music enough. The lines are long and uneven, and one is too wide for the page, so that "theirs," spills onto an indented line of its own. The poem seems to be running out of room. After this accumulation the last line is short and plain: "And then the song of each member of These States." The deflating "And then" makes the finish feel open, a door left ajar.
The second parenthesis darkens the mood. "(To the tap of the war-drum, if need be,)" is an odd phrase, because "tap" is such a small word for such a loud instrument. The understatement is chilling. The song of union may have to be sung to a military beat, and "if need be" admits that the unity he celebrates might one day have to be defended by force. The poem does not say what conflict he has in mind, but the aside shows he knows that "one and inseparable" is a hope as well as a fact.
The poem matters because it shows, in miniature, what Whitman was doing for poetry. He gave up rhyme and fixed meter for long, breath-like lines, and he turned a list of place names into a kind of anthem. He also let a single "I" speak for a whole nation without pretending the nation was uniform. That long, unrhymed, list-driven line became one of the most recognisable sounds in American poetry. It still has the pull of a journey that has only just begun.