Series 12 published by Frederick A. Stokes is the World’s Fighter Series illustrated by Twelvetrees. There are a total 4 cards in the series, all shown here-Germany, England, United States, and France. Germany’s soldiers are called Hoch Der Kaiser, England’s are Tommy Atkins, the United States are the Rough Riders with the famed Teddy Roosevelt, and France is the Old Guard. My favorite is the Rough Rider postcard because I think it is the cutest and I love Teddy Roosevelt. The cards were published in 1907, so they are pre-WWI.
The most interesting of the names to me is Tommy Atkins. According to Wikipedia, the term has been used since 1743, and the exact origin of the name is unknown. Germans would call out “Tommy” during the war if they wanted to communicate with a British soldier.