What is "graybacks"

Usage examples of "graybacks".

After the two armies had murdered each other for four or five days in the Wilderness, by fighting so close together that much of the time you could almost shake hands with the Graybacks, both hauled off a little, and lay and glowered at each other.

I tell you that as sure as there is a God who reigns and judges in Israel, before the Spring breezes stir the tops of these blasted old pines their Confederacy and all the lousy graybacks who support it will be so deep in hell that nothing but a search warrant from the throne of God Almighty can ever find it again.