The date--1972--implies Vietnam, and it is perfectly possible that "charging the cannon" was simply a poetic turn of phrase borrowed by the author to make it seem like an older song than it was, like false antiquing on mass-produced furntiture.

Aside from the reference to charging the cannons (which could also apply to charging entrenched enemy positions in any modern war) the language sounds contrived and modern, so I would suggest it is not about any earlier war in particular but a general song stirred up by the mind of a 70's-era songwriter by the storms of bad news, political fury, loss and confusion surrounding the slaughters of Vietnam. I think the words are inaccdurately transcribed, as wlel -- "he'd only fight me gun" makes no sense in any context except the American Civil War, but the language is not well chosen to reflect the era.

A