Just about all the major combatants of the Second World war (with the exception of the Italians) had atomic bomb programs, in some form. The "secret" of the bomb was not the science (the foundations of which had been laid out decades before) but in the creation of a stable bomb, and the methods of mass production, of same.
The Germans are usually thought ot have "missed" getting thebomb because of a mistake in process or proceedure, or because their scientists were starved of resources, etc. The real problem is that German scientists were aioming higher than the relatively puny A-bombs, and shooting straight for an "H-bomb" with few or no intermediate steps.
The Japanese handicaps were simply that the Japanese economy could not support the effort required for the basic research and infrastructure and that the Japanese mentality believed that victory in war came from spiritual, not material, means. That does not mean the Japanese did not make efforts to produce or acquire better weapons, but that once they had reached a certain level of technical proficiency, the will and means to carry it to it's next logical step often fell by the wayside. The Japanese were innovative, but certainly not INVENTIVE enough. That sort of mentality was almost-foreign to Japanese culture which prized conformity to originality(those who often were inventive were treated as one would treat nails that are sticking up: you hammer them down).