Juxtaposition, as a literary technique, can be very clear or extremely vague, since it consists of two or more ideas, places, characters, actions, or phrases placed side by side for the purposes of comparison and contrast. In some cases (such as Dickens’s “It was the best of times, it was the worst of times...”), this is clearly done to create a particular effect. However, until the piece of writing ends, everything must be beside something, so it is easy to find juxtapositions where no comparison of contrast was necessarily intended.
With this caveat, Claude MacKay’s “America” does have several images which present a clear contrast. The first two images contrast strongly, though they are both negative. At least “bread of bitterness” is some kind of sustenance, whereas sinking a “tiger’s tooth” into the poet’s throat sounds as though it would be fatal and is a far more violent, troubling image.
In the sixth line, because the poet’s strength is described as “erect against her hate” there is an image of both strength and hate standing up together to contend. Paradoxically, the strength is fed by the vigor of the country that is, at the same time, grinding the poet down, another instance of juxtaposition. This is followed by another double image, similarly unequal, of a rebel standing up against a king.
While the first juxtaposition created the sense of escalating violence against the poet, these images, pitting him against the hate of an entire country, then against “a king in state,” emphasize the inequality of any struggle between the poet and America.
The might of America is juxtaposed with its physical manifestations: the “granite wonders.” Manhattan island, to take the most obvious example, is mainly granite, which is why it can support so many skyscrapers, many of them at least partially constructed or faced with granite themselves, giving physical expression to the country’s wealth and power. However, the final juxtaposition of “Time’s unerring hand” and the “priceless treasures” of America contains a warning and perhaps a lament at the fact that even this great country, which the poet loves despite her rough treatment of him, cannot retain her power indefinitely.