Maybe during WW1 during the battle of belleau wood. I couldn’t tell if those uniforms are Marines or not, but the woods look like it might be.

I double checked, 5th Regiment was part of Belleau Wood. Places this around 1918, if accurate. Belleau Wood is also were Marines earned the nickname, devil dog. Germany said the Marines fought like hounds of hell, Tuefel Hunden.

It must be US(the poster, brig, is American) and judging by the helmet possibly Germany?