A friend of ours wrote the book “Wake Up America, WW1 and the American Poster” and he has an amazing collection of those posters which  are currently on display.  Today a group of friends met with him as he and his wife walked us through the exhibit.  It told a part of the story of how America entered and patriotically  recruited soldiers and volunteers for the war,  encouraged patriotism and  raised money to support the effort. These are three of the posters that I particularly liked.  The one on the right is by Howard Chandler Christy, who was in charge of recruiting   famous illustrators of the time to create these posters, the second was one was used to recruit African American soldiers, and the third is special because I had a great uncle who was in  the Air Service  in France.  
Altogether it was quite powerful.  Different war different era.  All frightening.