Leo Szilard invented the atomic bomb and reactor in 1933 as a
more efficient method of transmuting elements. It took
another 12 years plus a $2,000,000,000 investment by the US to
build the first bombs.
American scientists created the atomic bomb as a way to end World War II with a minimum amount of bloodshed. Though it caused approximately 130,000 deaths when it was dropped on Hiroshima, it is estimated that it saved over half a million lives by being the means by which the war was ended.