Conflicts and wars are not just fought with weapons, they are fought with words and pictures. From the caricatures that proliferated during the Napoleonic era to the twentieth century, graphical depictions have been generated for propaganda purposes. This collection of almost 3,000 posters, one of the largest online, is from the [U.S.] National Archives; they range from war bonds appeals to Nazi atrocities to the destruction of libraries. Vividly colorful with sparse verbiage, these were visceral calls to arms.
Another worthwhile collection is located at Northwestern University.