Many countries began to research nuclear weapons during WWII.
Efforts to promote non-proliferation began immediately following the war.
Even though it seems radical and extreme, I believe we missed the only chance mankind ever had to protect the world from inevitable nuclear devastation! My suggestion of how we could have stopped nuclear proliferation will give liberals, progressives, and the ACLU a coronary! Right after World War 2 the two super powers , the US, and the Soviet Union should have formed a joint task force to militarily prevent any other country from developing nuclear weapons! For the idealists that completely reject the idea of the two super powers using brute force to disallow nuclear proliferation, I guarantee you would have rather had that happen as what is inevitably going to happen sooner or later, and that is either a nuclear exchange by third world countries , or deliberate contamination by terrorists, either way, the world atmosphere will be trashed!