[fluffy0000]

Unconditional Surrender policy was adopted following the Casablanca Conference in Jan 1943, the Allies announced an unconditional surrender policy with respect to the Axis powers - ( Japan was part of the Axis powers which included Germany and Italy )

In 1943' the Allies including US, UK and Soviet Union agreed on almost nothing. But on the single point of ending WW2 with not just victory but also the pursuit of forcing the Axis powers into “Unconditional Surrender.”

(.., really pleased Stalin, going a long way to allaying his fears that his Western Allies might make a separate peace with Hitler.)

Before Japan was defeated both of Japans allies - Germany and Italy accepted “Unconditional Surrender”.
The application of “Unconditional Surrender” not only applied to the respective military of each Axis power but also to the entire country.
"..it was to assure for the foreseeable future that these countries would be unable to wage war again."