Our fuzzy buddies have been following armies to war for an awfully long time. I can't source this but you just know armor clad warriors heading for Bosworth Field trailed panting companions. They hung around, the ACW a little warmed by their presence.
With thanks to @LoyaltyOfDogs , MotM , for consistently bringing us slobbery, hirsute, enchanting common ground. Article from a Wisconsin paper, 1864.
Nothing to do with the ACW, just thought chickens deserved a shout out.