I see two refrains in this poem. They are "Do not weep" and "War is kind." Both of these refrains help to point to the major theme of the poem -- the idea that war is a devastating thing that destroys people's lives (and the lives of those who are left behind).
If war were really kind, the speaker would not have to tell the listener not to weep. But war, the ironic title of the poem notwithstanding, is not kind. It causes people great pain for no good reason, Crane says.
The poem is a strong and ironic antiwar statement. Stanzas 1, 3, and 5 focus on the losses (refrain) and deaths produced through war: A maiden loses her lover (lines 1–5), a baby loses her father (lines 12–16), and a mother loses her son (lines 23–26). There is nothing "kind" about the losses or about war. Stanzas 2 and 4 mock the symbols of passion that encourage war: booming drums, unexplained glory, the blazing flag of the regiment, the eagle on the flag. Both stanzas close with the same image of war’s reality: "A field where a thousand corpses lie." The realities of carnage and loss are thus contrasted with the illusions of ideals.