It's the American Civil war. Rural youth were heavily recruited. It's one of a hundred thousand family tragedies.

The imagined singer would have been in the 149th New York Infantry that was organized at Syracuse, N.Y. which mustered in September 18, 1862.

The Civil war was a horrific experience to the green recruits, who had never seen such sustained artillery and [some] Gatling gun firing. Explosive bullets were also used to terrible effect.

The "Letter to Syracuse" song perfectly expresses the soldier's cynicism and pessimism. He had "sowed last season's crop" along with his local friends, and the crop may never be harvested.