A war poet is usually defined as a poet who participates in a war and writes about his experiences. While the term is applied especially to those who served during World War I, it is documented as early as 1848, in reference to German revolutionary poet,Georg Herwegh. and is now applied to a poet writing about any war. However, Tennyson wrote probably one of the most famous war poems of the nineteenth century, and another non-combatant, Thomas Hardy, wrote major war poetry.
American Civil War
As the American Civil War was beginning, American poet Walt Whitman published his poem "Beat! Beat! Drums!" as a patriotic rally call for the North. Whitman volunteered for a time as a nurse in the army hospitals, and his collection Drum-Taps (1865) deals with his experiences during the War.
Probably the most famous nineteenth century war poem is Tennyson's "The Charge of the Light Brigade", which he supposedly wrote in only a few minutes after reading an account of the battle in The Times. As poet laureate he often wrote verses about public events. It immediately became hugely popular, even reaching the troops in the Crimea, where it was distributed in pamphlet form .
Rudyard Kipling's poem "The Last of the Light Brigade", written some forty years after the appearance of "The Charge of the Light Brigade", in 1891, focuses on the terrible hardships faced in old age by veterans of the Crimean War, as exemplified by the cavalry men of the Light Brigade, in an attempt to shame the British public into offering financial assistance. Various lines from the poem are randomly quoted by Mr. Ramsay in Virginia Woolf's To The Lighthouse.
Rudyard Kipling wrote poetry in support of the British cause in the Boer War,  includingthe well known "Lichtenberg", which is about a combatant's death in a foreign land. Swinburne, Thomas Hardy, and others wrote also poems relating to the Boer War.
World War I
The major novelist and poet Thomas Hardy (1840 – 1928) wrote a number of significant war poems that relate to both the Boer Wars and World War I, including "Drummer Hodge", "In Time of 'The Breaking of Nations'", and "The Man He Killed"; "[h]is work had a profound influence on other war poets such as Rupert Brooke and Siegfried Sassoon". Hardy in these poems often used the viewpoint of ordinary soldiers and their colloquial speech. A theme in the Wessex Poems (1898) is the long shadow that the Napoleonic Wars cast over the nineteenth century, as seen, for example, in "The Sergeant's Song" and "Leipzig". The Napoleonic War is the subject of Hardy's drama in verse The Dynasts (1904-08).
At the beginning of World War I, like many other writers, Kipling wrote pamphlets and poems which enthusiastically supported the UK's war aims of restoring Belgium after that kingdom had been occupied by Germany together with more generalised statements that Britain was standing up for the cause of good.
For the first time, a substantial number of important British poets were soldiers, writing about their experiences of war. A number of them died on the battlefield, most famously Edward Thomas, Isaac Rosenberg, Wilfred Owen, and Charles Sorley. Others including Robert Graves, Ivor Gurney and Siegfried Sassoon survived but were scarred by their experiences, and this was reflected in their poetry. Robert H. Ross describes the British "war poets" as Georgian poets. Many poems by British war poets were published in newspapers and then collected in anthologies. Several of these early anthologies were published during the war and were very popular, though the tone of the poetry changed as the war progressed. One of the wartime anthologies, The Muse in Arms, was published in 1917, and several were published in the years following the war.
David Jones' epic poem of World War I In Parenthesis was first published in England in 1937, and is based on Jones's own experience as an infantryman in the War. In Parenthesis narrates the experiences of English Private John Ball in a mixed English-Welsh regiment starting with their leaving England and ending seven months later with the assault on Mametz Wood during the Battle of the Somme. The work employs a mixture of lyrical verse and prose, is highly allusive, and ranges in tone from formal to Cockney colloquial and military slang. The poem won the Hawthornden Prize and the admiration of writers such as W. B. Yeats and T. S. Eliot.
In November 1985, a slate memorial was unveiled in Poet's Corner commemorating sixteen poets of the Great War: Richard Aldington, Laurence Binyon, Edmund Blunden, Rupert Brooke, Wilfrid Gibson, Robert Graves, Julian Grenfell, Ivor Gurney, David Jones, Robert Nichols, Wilfred Owen, Herbert Read, Isaac Rosenberg, Siegfried Sassoon, Charles Sorley and Edward Thomas.
In other countries
Canadian war poets of this period included John McCrae, who wrote In Flanders Fields, and Robert W. Service who worked as an ambulance driver for the Canadian Red Cross and was a war correspondent for the Canadian government.
Russia also produced a number of significant war poets including Nikolay Gumilyov (whose war poems were assembled in the collection The Quiver (1916)), Alexander Blok, Ilya Ehrenburg (who published war poems in his book "On the Eve"), and Nikolay Semenovich Tikhonov (who published the book Orda (The horde) in 1922).
The Spanish Civil War
The Spanish Civil War produced a substantial volume of poetry in English (as well as in Spanish). There were English-speaking poets serving in the Spanish Civil War on both sides. Among those fighting with the Republicans as volunteers in the International Brigades were Clive Branson, John Cornford, Charles Donnelly, Alex McDade and Tom Wintringham. On the Nationalist side, the most famous English language poet of the Spanish Civil War remains South African Roy Campbell.
World War II
By World War II the role of "war poet" was so well-established in the public mind, and it was anticipated that the outbreak of war in 1939 would produce a literary response equal to that of the First World War. The Times Literary Supplement went so far as to pose the question in 1940: "Where are the war-poets?" Alun Lewis and Keith Douglas are the standard critical choices amongst British war poets of this time. In 1942, Henry Reed published a collection of three poems about British infantry training entitled Lessons of the War; three more were added after the war. Sidney Keyes was another important and prolific Second World War poet.
Karl Shapiro, a stylish writer with a commendable regard for his craft, wrote poetry in the Pacific Theater while he served there during World War II. His collection V-Letter and Other Poems, written while Shapiro was stationed in New Guinea, was awarded the Pulitzer Prize for Poetry in 1945, while Shapiro was still in the military. Shapiro was American Poet Laureate in 1946 and 1947. (At the time this title was Consultant in Poetry to the Library of Congress which was changed by Congress in 1985 to Poet Laureate Consultant in Poetry to the Library of Congress.). Also, while serving in the U.S. Army, the American poet Randall Jarrell published his second book of poems, Little Friend, Little Friend (1945) based on his wartime experiences. The book includes one of Jarrell's best known war poems, "The Death of the Ball Turret Gunner." In his follow-up book, Losses (1948), he also focused on the war. The poet Robert Lowell stated publicly that he thought Jarrell had written "the best poetry in English about the Second World War."
The Vietnam war also produced war poets, including Michael Casey whose début collection, Obscenities, drew on his work as military police officer in Vietnam's Quang Nga province. The book won the 1972 Yale Younger Poets Award. Other prominent Vietnam War poets include W. D. Ehrhart, Yusef Komunyakaa, and Bruce Weigl.
Most recently, the Iraq War has produced war poets including Brian Turner whose début collection, Here, Bullet, is based on his experience as an infantry team leader with the 3rd Stryker Brigade Combat Team from November 2003 until November 2004 in Iraq. The book won numerous awards including the 2005 Beatrice Hawley Award, the 2006 Maine Literary Award in Poetry, and the 2006 Northern California Book Award in Poetry. The book also was an Editor's Choice in The New York Times and received significant attention from the press including reviews and notices on NPR and in The New Yorker, The Global and Mail, and the Library Journal. In The New Yorker, Dana Goodyear wrote that, "As a war poet, [Brian Turner] sidesteps the classic distinction between romance and irony, opting instead for the surreal." 
- "war poet noun" The Oxford Dictionary of English (revised edition). Ed. Catherine Soanes and Angus Stevenson. Oxford University Press, 2005
- Herwegh, Georg, The Columbia Encyclopedia (2008)
- The Times, Southern Germany, 29 September 1848
- Callow, 283
- Callow, 293
- Alfred Lord Tennyson, Poems, ed. Hallam Lord Tennyson and annotated by Alfred Lord Tennyson (London: Macmillan, 1908), II, 369.
- Brighton, Terry (2005), Hell Riders: The True Story of the Charge of the Light Brigade, Penguin
- Carrington, C. E., (1955) The life of Rudyard Kipling, Doubleday & Co., Garden City, NY, p. 236
- Craig Raine (ed.), Kipling, Selected Poetry (Penguin, 1992), pp. 214–215
- Time's Laughingstocks and Other Verses (London: Macmillan, 1909)
- Axelrod, Jeremy. "Thomas Hardy". The Poetry Foundation. Retrieved 2014-05-19.
- Katherine Kearney Maynard, Thomas Hardy's Tragic Poetry: The Lyrics and The Dynasts. Iowa City: University of Iowa Press, 1991, pp.8-12.
- Gilmour, David, The Long Recessional: The Imperial Life of Rudyard Kipling, London: Farrar, Straus and Giroux, 2002
- Richard Perceval Graves, ‘Graves, Robert von Ranke (1895–1985)’, Oxford Dictionary of National Biography, Oxford University Press, 2004
- The Georgian Revolt, p.166.
- Dilworth, Thomas. Reading David Jones. Cardiff: University of W Wales, 2008, p. 1; Dilworth, Thomas. The Shape of Meaning in the Poetry of David Jones. Toronto: University of Toronto Press, 1988; Eliot, T.S. "A note of introduction," In Parenthesis. By David Jones. London: Faber, 1961, vii.
- Westminster Abbey: Poets of the First World War
- R.R. Milner-Gulland in A.K. Thorlby (ed.), The Penguin Companion to Literature: European (Penguin, 1969), p. 762.
- The Penguin Book of Spanish Civil War Verse, edited by Valentine Cunningham (Penguin, 1980); see also War Poets Association: Spanish War
- Poems from Spain: British and Irish International Brigaders of the Spanish Civil War in Verse, edited by Jim Jump. (London: Lawrence & Wishart, 2006)
- Blythe, Ronald (1966). Components of the Scene. Harmondsworth: Penguin.
- London Review; Andrew Sinclair, The War Decade: An Anthology Of The 1940s. London; Hamish Hamilton. ISBN 0241125677 (p. 47)
- Press, John (1 March 1994). "Poets of World War II". In Scott-Kilvert, Ian. British Writers: 007. New York: Charles Scribner's Sons. pp. 422–423. ISBN 978-0684166384. Retrieved 25 May 2015.
- Scannell, Vernon Not Without Glory Woburn Press , London 1976 ISBN 0713000945
- Gilroy, Harry. "Poets Honor Memory of Jarrell at Yale." The New York Times 1 March 1966.
- W. D. Ehrhart, The Madness of It All: Essays in War, Literature and American Life, (Jefferson, NC: McFarland & Company, 2002) pp. 141-172.
- Unaccustomed Mercy: Soldier-Poets of the Vietnam War, edited by W. D. Ehrhart. (Lubbock, Texas: Texas Tech University Press, 1989)
- Lorraine Ash, A Poet Goes to War, September 17, 2006
- Book Publisher's Site Info on Book
- New Yorker Article
- Silkin, Jon. Out of Battle: The Poetry of the Great War. Basingstoke: Palgrave Macmillan, 1972. Rpt. 1998. ISBN 978-0-312-21404-3.
- Roy, Pinaki. The Scarlet Critique: A Critical Anthology of War Poetry. New Delhi: Sarup Book Publishers Pvt. Ltd., 2010. ISBN 978-81-7625-991-0.
- Ghosal, Sukriti. War Poetry- The New Sensibilities. Kindle Edition, 2015. ASIN: B00XH4O74Q. http://www.amazon.com/War-Poetry-The-New-Sensibilities-ebook/dp/B00XH4O74Q.
- A selection of Boer War poems 
- War Poems From Iraq
- War Poets Association
- The First World War Poetry Digital Archive
- The pro-war 1917 pamphlet Pro Patria (1917) by Philadelphia poet Florence Earle Coates (1850–1927)
- Echenberg Collection of over 5000 volumes of War Poetry