Which war did John McCrae fight in when he wrote his famous poem?

John McCrae fought in World War I when he wrote his famous poem "In Flanders Fields." This poem was composed during the war while he served as a medical officer in the Canadian Expeditionary Force. The poem reflects on the horrors of war, the sacrifices of soldiers, and the symbolic significance of poppies, which grew in the fields where many battles took place.

The context of World War I is crucial as it was marked by trench warfare, significant loss of life, and profound changes in societal attitudes towards war. McCrae's experiences on the front lines deeply influenced his writing, making his poem a poignant reminder of the sacrifices made during this tumultuous period. The other wars listed—World War II, the Korean War, and the Vietnam War—occurred later and are associated with different historical contexts and themes, which do not link the poem in question to McCrae's experiences.