"War Is Kind"? No, it's not, but a poem with this title is definitely all about war, no matter how mean it is. Yep, war is very unkind; it takes lovers from their maidens, fathers from their children, sons from their mothers. It causes nothing but death, heartbreak, loss, in short all kinds of bad stuff. And even though wars are no good, they keep on happening, largely because there are always people, like the guy in the second and fourth stanza, who, according to Crane, are all to willing to send soldiers to their deaths.
This poem is about how all war does is destroy families; the relationships between maidens and lovers, babes and fathers, and mothers and sons are all destroyed by war.
Crane argues that wars continue to happen because military strategists, generals, and the like don't see soldiers as real people; they only see them as born to drill and die, like cattle.