Short answers, pulled from the story.
Walt Whitman heard that President Abraham Lincoln had been shot on the 14th of April 1865 while standing in the yard of his mother's home. He stepped outside to find lilacs blooming as news of the assassination spread across a grieving nation.
Whitman contracted with Gibson Brothers to produce a pamphlet titled Sequel to Drum-Taps containing eighteen poems including When Lilacs Last in the Dooryard Bloom'd. The fourth edition of Leaves of Grass published in 1867 by William E. Chapin absorbed these poems as a supplement and contained five different formats.
Three prominent motifs form a trinity within the text: lilacs representing perennial love, a fallen star symbolizing Lincoln, and a hermit thrush embodying death itself. Biographer David S. Reynolds describes these images as autobiographical elements woven into the narrative.
Scholars believe T.S. Eliot drew from Whitman's elegy when fashioning his poem The Waste Land published in 1922. Eliot prominently mentions lilacs and April in opening lines plus passages about dry grass singing where hermit-thrush sings in pine trees.
Charles Villiers Stanford set the poem first in Elegiac Ode Opus Twenty-One published in 1884 for baritone soprano chorus and orchestra. Paul Hindemith composed When Lilacs Last in Dooryard Bloom'd Requiem commissioned by Robert Shaw Chorale to mourn Franklin Delano Roosevelt dying the 12th of April 1945.