Applying theoretical nuclear physics to build a bomb, the Manhattan Project made use of fission or splitting the atom, to create a weapon that would create an incredible amount of destruction when dropped on Japan. Because of the scale of the destruction at both Hiroshima and Nagasaki, ‘Total War,’ a concept that resulted from this type of destruction, was introduced. Because of this new concept of ‘Total War,’ military doctrine shifted from ‘active combat’ to ‘nuclear deterrence’ and ‘Mutually Assured Destruction.’
PC: Wikipedia