The United States built an industrial infrastructure equal in size to its entire automobile industry in order to conduct research and more crucially refine enough radioactive isotopes to build just the three atomic bombs. This was while recapturing imperial possessions in Africa and across the pacific, managing the biggest amphibious operation in history, sinking the powerful Japanese Imperial Navy, winning the immensely research-intensive Battle of the Atlantic, running their own highly effective submarine campaign against Japanese supply, and maintaining two strategic bombing campaigns of enormous scale.
Axis and Allies doesn’t have the atom bomb because researching it would have to be so goddamn expensive that only a historically accurate United States could afford it. And, If the United States has 120 IPCs every turn they’re not going to bother spending the necessary 200 IPCs over 5 turns or whatever developing the atomic bomb because Axis and Allies players have no regard for the lives of their little plastic soldiers.
It wasn’t a matter of research so much as production of the needed isotopes, the Germans knew how to build a bomb, but how were they supposed to match the kind of expenditure the United States made, particularly when all of their production areas were subject to strategic bombing?
So as a house rule I’d have to say the atomic bomb only really makes sense as
“If the game reaches round n without victory conditions being met, then the Allies win.”
Which is both a major buzzkill and pretty much already how it shakes out…