Not exactly an anti-war song, I guess, bot not pro-war either:

Archie Fisher set music to this little Burns poem on his ORFEO album many years ago, singing it as only he can. I've always liked this little gem....

Silver Tassie

Gae bring tae me a pint o' wine
And fill it in a silver tassie
That I may drink, before I go
A service tae my bonnie lassie

   The boat rocks at the pier o' Leith,
   Fu' loud the wind blaws frae the Ferry
   The ship sails by the Berwick-Law
   And I maun leave my bonnie Mary

The trumpets sound, the banners fly
The glitt'rin' spears are ranked an' ready
The shouts o' war are heard afar
And the battle closes deep and bloody

   Tis not the roar o' sea on shore
   Wad mak' me langer wish tae tarry
   Nor shouts o' war that's heard afar
   But leaving thee, my bonny Mary