In the Fantastic Beasts and Where To Find Them film, it is mentionned that Newt Scamander's brother, Theseus, is a war hero. In another part, as Jacob meets wizards, they all seem to be impressed that he fought in it.
Although it seems improbable that WWI would pass unnoticed by the wizarding world, there aren't other clues as to whether other wizards participated in the war (at least in the MACUSA community).
So, did wizards participate in the First World War? Fighting each other or influencing the battles of their non-magic counterparts?