While it does break from traditional rhyme and meter, it is written in a specific form called "vers libre". Vers libre is a type of poetry that uses free rhythm but still maintains a definite structure.
"Chicago" has:
* A distinct rhythm and cadence: Sandburg uses repetition, assonance, and alliteration to create a rhythmic flow.
* A consistent structure: The poem is divided into short, uneven stanzas with a distinct flow.
* A strong sense of meter: While not traditional, the poem uses a specific meter to create a sense of momentum.
While not strictly free verse, "Chicago" is considered a masterclass in vers libre, showcasing the power of rhythm and structure even when breaking from traditional poetic forms.