[okie01]

Japan [was not] in WW1 as that nation was not involved in the fighting

Actually, Japan was involved in WW I -- on the side of the Allies, fighting against Germany.

That's how Japan came to own the Marianas, Caroline and Marshall Islands, along with Tsingtao on the Chinese mainland. All had been German colonies.

Japan during World War I

[jmacusa]

Japan didn’t do any fighting on the European landmass.