How did the US justify its decision to use atomic bombs against Hiroshima and Nagasaki?

It is,
perhaps, historically inaccurate to say that the US justified its decision at the time that it
was made.  At the time, there was almost no controversy over the use of the bomb.  Winston
Churchill reported, for example, that it was simply assumed that the US would use any weapon
that it had to win the war.  The idea...