A socialist worker raises the red flag, adoring crowds greet Hitler and Mussolini, and Uncle Sam orders Americans to enlist: In the first half of the 20th century, images were circulated by the millions on postcards intended to change minds and inspire actions. Whether produced by government bureaus, publishers, aid organizations, or resistance movements, these postcards—350 of which are shown and discussed here—conveyed their messages with striking graphics, pithy slogans, and biting caricatures.