While we're sharing anti-war songs/poetry, I like And The Band Played Waltzing Matilda (originally written by Eric Bogle, but I personally like the Pogues' version): https://www.youtube.com/watch?v=PKURhqmSLmM

The Australians have some incredible anti-war music. Redgum's /I was only 19/ is brutal: https://www.youtube.com/watch?v=1UYDKxxQ50o