Civil War armies were the most literate in history to that time. I believe that most sources give the northern literacy rate as 85% to 90% with the South coming in a little lower at 80%. The main reason for the lower rate in the South was the lack of free public education.
I think you may be looking at the political cartoon from the wrong angle. I believe it had the same affect on the populace as similar cartoons do today. A satirical soundbite that immediately grabs attention and piques curiosity, the cartoon is a quick way to both deliver and receive an image of a political personage or an event. Thomas Nast, the creator of Santa Clause, began his career as a satirical illustrator.
A good book on the illustrators of the CW era is <u>The Image of War The Pictorial Reporting of the American Civil War</u> by William Thompson. I found a couple of minor errors in the book which was published in 1959 and re-released in 1989. It is possible the errors were the result of unavailable information at the time. It is, however, one of the few books that treats this subject specifically. The book is availble on ABE books at reasonable prices.
Connie Boone