War poetry
The term war poet came into currency during and after World War I. A number of poets writing in English had been soldiers, and had written about that experience. Quite a number had been died, most famously Rupert Brooke and Wilfred Owen. Others such as Siegfried Sassoon had survived, but made a reputation based on scathing poetry written from the disabused point of view of the trench soldier who had lost faith in his military superiors.
There was probably at least as much poetry of quality written on the German side of the Western Front; but it was in English poetry that the war poem became an established genre marker, and attracted growing popular interest. Americans and Canadians contributed notable work, and the French had their own war poetry. It is perhaps not a well-defined question, what makes a war poet (compare, say, Brooke and Georg Trakl). The public may have seen war poems as reportage and direct emotional links to the soldier. Robert Graves served in the trenches and survived, David Jones also; Graves did not use war experience as poetic material (making it autobiography in Goodbye to All That), and Jones postponed its use, incorporating it into modernist forms.
The Spanish Civil War produced a substantial volume of poetry in English and, of course, Spanish too — there were English-speaking poets serving on both sides. By the time of World War II the role of 'war poet' was so well-established in the public mind that 'where are the war poets?' became a topic of discussion. Alun Lewis and Keith Douglas are the standard critical choices amongst English-language war poets of that time; there was probably more heavyweight poetry written in French from 1939-1945, than in English. The reason may be to do with the onward march of technology and the fact that soldiers spent less of their time sitting in trenches waiting for something to happen.
The expectation of war poetry can be noted in a character from the C. S. Forester novel The Ship who is a poet serving in a Royal Navy ship in the Mediterranean around 1942, and who is killed in action. Benjamin Britten's War Requiem made use of war poem texts. There has been little recognition of war poetry from any subsequent conflict, certainly when compared with novels.