The Most Dangerous Man in America: The Making of Douglas MacArthur by Mark Perry

The Most Dangerous Man in America zeroes in on what might be called the critical years of MacArthur's military career -- the close to 13 years of FDR's presidency.

Boiled down it's the story of creative conflict -- between FDR and MacArthur through those years, and between MacArthur in command of the army and Ernest King from the navy over who should run the campaign against Japan.

In both cases the competition sparked creativity -- and ultimately better results if there had been no competition.

A fairly even assessment of MacArthur -- it looks at the good and bad -- it's the perfect prequel to Supreme Commander (which picks up the story after the war and during the occupation of Japan.) 
MacArthur was complex - and The Most Dangerous Man in America explains some of that in a compelling way.