Steeleye Span's song sounds a bit like an extended version of "Johnny has gone for a soldier"

A another song of rather similar content is "Off to Flanders" in Alfred Williams' 'Folk Songs of the Upper Thames'. This stems from a broadside ballad, probably of 1691, when the English were fighting in Flanders, "The Farmer's Son of Devonshire", in my internet broadside ballad index at ZN2772.

Another anti-war one is the short, but pity, "Will you go to Flanders, my Molly, Oh" in Herd's Scots Songs, 1776. The tune of this later became known as "Gramachree Molly", and "The harp that once through Tara's hall".