The poem ‘Small Pain in My Chest’ is all about the pity of war. And the term ‘Asian dirt’ in the poem refers to the Vietnam War (1955-1975) after which the poem was written (1983). Our poet was very much moved by the pain and emotions of the soldiers, by the destruction and loss of lives it caused, and decided to convey his message through this poem. This is all about the historical background.
But an American magazine published the poem with slight change. It replaced ‘Asian dirt’ with ‘Southern dirt’ to refer to the US Civil War. Understandably they meant that all soldiers are the same — their sufferings and feelings are similar wherever they fight. Thus the poem is an anti-war poem in its broader sense and is against all wars.