I think WWI impacted Tolkien more than WWII seeing as that was the war he was in, and the one that caused the deaths of many of his friends. Much of his history of middle earth was written before Hitler rose to power. However, the LOTR story does appear to be “tacked on” at the end of the second age and has no connection at all with the first age (aside from characters Galedriel, Sauron and Elrond)so maybe there was some reflection of current events to it.