War has long figured as a theme in poetry—after all, some of the world's oldest surviving poems are about great armies and heroic battles. But while Homer may have idealized his combatants and revered their triumphant, incessant fighting, the treatment of war in poetry has grown increasingly more complex since then.

The numerous conflicts of the twentieth century produced poets, including those who served as soldiers in World War I, who turned their pens to documenting the tragic effects of war. Other poets have concentrated their writing on the horrifying impact of war on civilians. In Pablo Neruda’s famous poem about the Spanish Civil War, "I Explain a Few Things," he discards metaphor entirely to say: "in the streets the blood of the children / ran simply, like the blood of children." At the end of the poem he implores the reader to look at the devastating results of war:

Come and see the blood in the streets,
come and see
the blood in the streets,
come and see the blood
in the streets!

Likewise, in "The Diameter of the Bomb," Israeli poet Yehuda Amichai finds that poetic descriptions can falter and fail in the face of violent tragedy:

And I won’t even mention the howl of orphans
that reaches up to the throne of God and
beyond, making
a circle with no end and no God.

Some poets have focused on another devastating effect of war: the fear engendered when citizens and nations are forced to take sides, to answer the questions, who is "good?" who is "evil?" C. P. Cavafy explored this problem in his allegorical poem "Waiting for the Barbarians," written in 1898. The poem describes a citizenry so fully afraid of a barbarian invasion that the society has stopped functioning. The poem concludes:

Why this sudden bewilderment, this confusion?
(How serious people’s faces have become.)
Why are the streets and squares emptying so rapidly,
everyone going home lost in thought?

Because night has fallen and the barbarians haven’t come.
And some of our men just in from the border say
there are no barbarians any longer.

Now what’s going to happen to us without barbarians?
Those people were a kind of solution.

Other poets have recognized the ironic blurring of opposing forces that often occurs in wartime. Yusef Komyankaa's book Dien Cai Dau, for example, written from the perspective of an African-American soldier fighting in Vietnam, includes the poem "Tu Do Street," which describes not only the relationship between Vietnamese and American soldiers, but also black and white soldiers:

Back in the bust at Dak To
& Khe Sanh, we fought
the brothers of these women
we now run to hold in our arms.
There’s more than a nation
inside us, as black & white
soldiers touch the same lovers
minutes apart, tasting
each other’s breath,
without knowing these rooms
run into each other like tunnels
leading to the underworld.

Finally, in the face of irrational and unthinkable destruction, such as genocide, the space of words becomes a problematic one, and language appears to dissipate. The poet Paul Celan, who survived the Holocaust, often struggles with describing the events he witnessed and how to escape them, as in his famous poem "Death Fugue":

Black milk of daybreak we drink it at sundown
we drink it at noon in the morning we drink it at night
we drink and we drink it
we dig a grave in the breezes there one lies unconfined

How do people recover from the devastating conflict of war, especially if their homelands have been ravaged? In "Foundations," the Polish poet Leopold Staff describes how his attempts to "build" have "tumbled down," concluding: "Now when I build, I shall begin / With the smoke from the chimney."

For more poems about war, consider the following:

"In Flanders Fields" by John McCrae
"The Soldier" by Rupert Brooke
"Dulce Et Decorum Est" by Wilfred Owen 
"The Diameter of the Bomb" by Yehuda Amichai
"Memorial Day for the War Dead" by Yehuda Amichai
"God Has Pity on Kindergarten Children" by Yehuda Amichai
"The Fall of Rome" by W. H. Auden
"On Being Asked to Write a Poem Against the War in Vietnam" by Hayden Carruth
"Waiting for the Barbarians" by Constantine Cavafy
"Navy Field" by William Meredith
"Death Fugue" by Paul Celan
"War is Kind" by Stephen Crane
"The Czar's Last Christmas Letter: A Barn in the Urals" by Norman Dubie
"Spoken from the Hedgerows" by Jorie Graham
"Elegy for Fortinbras" by Zbigniew Herbert
The Iliad by Homer
"Eighth Air Force" by Randall Jarrell
Dien Cai Dau by Yusef Komunyakaa
"Notes for an Elegy" by William Meredith
"War Music (an account of books 16-19 of Homer's Iliad)" by Christopher Logue
"For the Union Dead" by Robert Lowell
"My Father on His Shield" by Walt McDonald
"The War Works Hard" by Dunya Mikhail
"I Explain a Few Things" by Pablo Neruda
"Poem" by Muriel Rukeyser
"Foundations" by Leopold Staff
"Starvation Camp Near Jaslo" by Wislawa Szymborska