I guess no one knows.
It's hard to say, it looks pretty much like every map case of the era.
It could be French, British, US... Most British officers carried similar ones in WW1, but they were all private purchase.
Does it have markings?
There is no markings at all on it.
So you do think it is ww1.
are the buttons marked?
Hmmm (Nice shots and thanks) all I can add is - Eastern European or Russian?