How and why the US developed the atomic bomb?
There were probably two underlying reasons: The Manhattan
project takes care of how. Why was more complex, there was a fear
Axis was already making an effort to produce atomic weapons and
Allies would have to counter this potential threat, and there was a
knowledge that with enough time, money and effort an atomic
could and would be produced to end World War 2 with the United
in a preeminite position.