"Unser Volk in Waffen" is one of the German classics written about the First World War. I believe Christian Speyer did the illustrations, which are some of the best military depictions out there. His drawing style reminds me of the work of one of his famous contemporaries, Paul Casberg, a personal favorite. Those are some fabulous uniform studies that you've posted, talk about photo-realism with a pencil.
The postcards have that distinct imperial look to them, there's a feeling to these images that's somehow almost tangible? The Hohenzollern/German eagle chasing the proud French cock back over the border is mindful of the Belgians herding the German swine home, too. Very powerful in black and white, it immediately focuses one's attention on the two birds and the banner headline, "Steadfast and True, The Watch Over the Rhine..."
The second illustration makes me think of the artwork that's found on German military beersteins. Very colorful line-art of the artillery boys bombarding the Fortress of Reims. Great use of the searchlight's cone of vision to highlight the stronghold, the wisps of smoke playing through the light are especially well rendered.
