The digital collection World War I Postcards from the Bowman Gray Collection has been created by the library of the University of North Carolina at Chapel Hill. The collection contains some 6,400 postcards from the main belligerent countries (United Kingdom, France, Germany, Belgium, Russia and Italy), but also from other countries. The sheer number of postcards in this collection is equivalent to the number of interesting subjects, for example cavalry or children. Some commercial series, too, are completely present. You can browse the collection in its entirety (530 records with often multiple items), choose among the subjects, names and places, or use the free text search. The general introduction to this collection gives also a succinct bibliography on the subject of First World War postcards.