Applying theoretical nuclear physics to creating the bomb, the Manhattan Project used fission, or splitting the atom, to create a weapon that would create an incredible amount of destruction if dropped on Japan. Due to the scale of destruction in both Hiroshima and Nagasaki, the concept of ‘total war’ was introduced which resulted from such destruction. Due to this new concept of ‘total war’, military doctrine shifted from ‘active war’ to ‘nuclear deterrence’ and ‘mutually assured destruction’.
PC: Wikipedia