It draws on the diaries and memoirs of those closest to Emperor Hirohito, documents which only emerged after his death 11 years ago.
A new book published on Sunday in the United States is expected to stir up renewed debate in Japan over the wartime role of the Emperor Hirohito.
The American historian Herbert Bix, who is based in Japan, draws on recent documents to argue that the emperor played a direct role in the war and was not the powerless figurehead he is often portrayed to have been.
The book, called Hirohito and the Making of Modern Japan, argues that the failure to prosecute the emperor after the war still has important implications for the Japanese.
Even today, more than half a century after it ended, the war in Asia and particularly the role of the emperor, remain highly sensitive subjects in Japan.
A brutal image
The media rarely tackles the issue and intellectuals and historians are often circumspect in what they say.
But it will be hard for them to ignore the new book by Herbert Bix.
It draws on the diaries and memoirs of those closest to Emperor Hirohito, documents which only emerged after his death 11 years ago.
The book directly challenges the traditional Japanese view of the emperor as a peace-loving botanist.
He is described as a dynamic activist who emerged by the end of the 1930s as a real military commander, giving direct orders for the brutal campaign in China.
He is said to have received daily battle reports and to have legitimised Japan's push for expansion throughout East Asia.
Professor Bix says the failure to prosecute the emperor at the end of the war and the deliberate falsification of his role has made it difficult for the Japanese to deal with their past and he says many organisations are still reluctant to address the issue because of threats by right-wing thugs who tolerate no criticism of the imperial family.
No Japanese publisher has yet come forward to translate the book.
It is not the first time that Hirohito has been portrayed as something more than a powerless figurehead but the evidence presented this time will be hard to refute.