An alternate history of WWII where Japan wins. It's written for history buffs and wargamers. It discusses a variety of alternate histories. For instance, more effective Nazi diplomacy gets the Japanese to attack the Soviets rather than the Americans. This scenario actually makes some sense. The Nazi's came very close to crushing the Soviets in the first year. Had the Japanese attacked in Siberia it might well have tipped the balance. The last German drive on Moscow was stopped by reserves that Stalin pulled out of Siberia. If the Japanese had gone on the offensive, those reserves would not have been available.
Other than that, the idea that Japan could defeat a United States with a larger, loyal, and warlike population, vastly greater national territory, advanced technology, massive industry, and plentiful farmlands is foolish. Admiral Yamamoto understood this, no other senior Japanese leader did.
What the book does highlight is how slender the US margin of victory was. At Midway had a lost American air strike turned south to look for the enemy instead of north, or had a Japanese cruiser's floatplane got airborne on time, the Japanese might have won. Had a Japanese admiral had a little more Samurai spirit, the battle of Leyte Gulf would have been a famous Japanese victory.
A fun read.