The association between war casualties and poppies arose from the opening lines of the poem, In Flanders Field:
"In Flanders fields the poppies blow; Between the crosses, row on row".
John McCrae, a Canadian army officer, wrote the poem from the viewpoint of the dead soldiers. McCrae wrote it during the Second Battle of Ypres, the day after he helped to bury a close friend. Noticing the way poppies bloomed around the graves, he included this observation in his poem.