Embracing Defeat: Japan in the Wake of World War II by John W. Dower

This is an amazing history that explains the Japan of today (though published in 1999) by peeling back how both Japan and the United States reacted to the results of the Second World War.
It's a complex and intricate relationship and it is thoroughly explored here.

What we see is a victor nation and a defeated one navigate their way to what turned out to be a better future for them both and for the world.

This is also a great companion read with Hirohito (by Herbert P. Bix) and In the Realm of the Dying Emperor (by Norma Field) since they all fit together as a compelling 20th Century portrait of Japan.