Charles H. Maasberg was born on July 2nd, 1894 in Wisconsin and enlisted for the draft on June 5th, 1917. Although I can’t be sure when he was sent overseas, I can deduce that he was assigned to an ordnance handling unit. He rose to the rank of Sergeant by 1919, and returned home to the US soon thereafter. This wonderful outdoor posed shot was taken in France in 1918, and shows Charles posing in a hand-knit sweater complete with tie. I can only imagine that it was taken in the backyard of a rural French home given the broken flower pots and creeping vines on the wall. The lack of foliage may help us date the photo to the fall or winter months. This would date the photo to the September-November of 1918 period.
1917 Draft Card
Portraits of War 
Ack, your photo identifications are cooler than mine!
Maasberg is a typical Dutch/Belgian name. Maybe another lead for more research?
…or German. His father immigrated to the US from Germany.