German; 19th(1st Wurttemberg) Uhlans "König Karl" Uhlan, Raised 1683, Home Depot; Ulm. XIII Army Corps. Read here https://www.flickr.com/photos/paranoid_womb/12467217424/in/photostream/ the process used by Paranoid -Womb used to identify the unit depicted in this unmarked photograph
A sentry post of the French Army in the advanced lines on the Macedonian front. The Macedonian Front, a.k.a. the Salonika Front, remained quite stable, despite local actions, until the great Allied offensive in September 1918, which resulted in the capitulation of Bulgaria and the liberation of Serbia.