I suggest the book The Rising Sun: The Decline and Fall of the Japanese Empire 1936-1945, for topics involving the Empire of Japan. I find it harder to get my hands on less bias sources on the Empire of Japan for this period of history, and it is one of my “go to books” on the subject. Also, almost anything from Donald Keene, likely one of the foremost experts on Japan today, might be helpful. His book on Meiji could be a good source for the Empire of Japan’s coming into the 20th Century (since HIM the Emperor Meiji died in 1912). Lastly, while I have only read excerpts, James B. Crowley seems like a good source that another gentleman that I have read in the past on Japan during this period has used, and maybe worth looking into.
Hope this is helpful. The Empire of Japan from the Meiji Era to the Showa Era is a personal hobby and love of mine, and hope these source can be helpful to you all to make the best view possible.