which battle took place first,  Battle of Belleau Wood or Operation Diadem ?
Battle of Belleau Wood: The Battle of Belleau Wood (1–26 June 1918) occurred during the German Spring Offensive in World War I, near the Marne River in France. Operation Diadem: Operation Diadem, also referred to as the Fourth Battle of Monte Cassino or, in Canada, the Battle of the Liri Valley, was an offensive operation undertaken by the Allies of World War II (U.S. Fifth Army and British Eighth Army in May 1944, as part of the Italian Campaign of World War II.
Battle of Belleau Wood