I don't know why the term "cracker" seems to be primarily a Georgia term or how it actually began. But the common understanding of the term as I grew up using it is to describe the poor, lower class white farmers eeking out a living on poor land. They were uneducated but hard-working, although not necessarily innovative or entrepreneurial. They were shrewd and crafty but not dishonest.
"Crackers" should never be confused with "poor white trash" -- that's another class of people entirely.
That crackers were considered to possess the best characteristics of the common man is born out by the fact that Georgia's semi-professional baseball team in the Fifties was called the "Atlanta Crackers." Also, one of the most sympathetic characters in Gone With The Wind was Will Benteen, who married Scarlett's whiny sister SueEllen. Will was a cracker who without any education or managerial experience brought Tara back after the war to something approaching its prior glory -- without using slave labor, of course.
People who use the word "cracker" as a put-down are uninformed as well as incredibly insenstive. And usually elitist snobs.
I don't know why the term "cracker" seems to be primarily a Georgia term or how it actually began.Actually, Iwo Jima, it's more of a Florida term. It evolved to describe the cowboys of the 19th Century who drove cattle to market across the scrub wilderness of Central and South Florida, "cracking" their whips as they rode. Many of these folks (including some of my own) migrated to Florida from Georgia (Wiregrass, here), and became part of the Florida culture.
As you may know, Florida provided most of the food, meat, vegetables, sugar, salt, etc. to the Confederacy during the War Between the States, and the cattle drives were very important. Many of them are still re-enacted in S. Central Florida nowadays.