Over 16 million people died in battle or were civilian casualties of the war.
John McCrae was a Canadian doctor. He served as as a Lieutenant-Colonel in the war.
The poem was published in 1915, and its immediate success led to it being quoted in propaganda as part of the war effort. The reference, in the poem, to the red poppies of Flanders has led to the the symbolic significance of the wearing of poppies on Remembrance Day each year.
John McCrae died of pneumonia during combat action in 1918, just eight months before the war ended.