Searching by genres of ephemera such as advertisement, poster, invitation, postcard, etc reveals just how much ephemera is on the site (1000 results for poster, for example). Searches can be narrowed by country and classification. Full advanced searching is available including limitation by date. The screen shot shows a search for poster and war, sorted by date. As the content is so international, this is a wonderful resource for comparing national graphic styles.
There is also an ARTstor blog.