One definition of cracker is:
'cracker - a piece of hardtack; the name had nothing to do with "Cracker," a derogatory nickname that Georgia
plantation owners had for upcountry farmers, whose wheat had to be "cracked" before it could be used.'
In 1863 Grant used a route, to supply the USA forces nearly surrounded in Chattanooga, which became known as
the 'Cracker Line'.
Some more Civil War Slang