Why did the United States create the Manhattan Project and begin the process of a nuclear reactor and an atomic bomb?
Basically it was because the Jews who assisted had fled for their lives from Nazi :Germany and they knew of a German push to get THEIR own atomic bomb. The Manhattan Project was the very first nuclear arms race. Hitler has pushed for Germany to have the first nuke, even as he and most of the world could barely understand the science and theories from Albert Einstein.
When Germany fell, it was discovered their scientists were maybe 30 years away from creating a nuke. But General Groves, head of the Manhattan Project, wanted to drop the two bombs: Fat Man and Little Boy. Japan refused to surrender and a major allied invasion of the Japanese mainland was in the planning stage. Groves originally wanted to target Kyoto, but Secretary Stimson forbade it.
Robert Oppenheimer had doubts about using the nuke. If it didn't work, the Japanese would have a model to create one. If it did work, it would create a massive arms race.
Safer world? In the 80s (when everyone was REALLY scared of global nuclear war) there was an acronym MAD: Mutual Assured Destruction.
Since the incineration of Hiroshima and Nagasaki, there has been nuclear proliferation all over the world, in all the countries you just mention. But there has not been ONE SINGLE NUCLEAR BOMB deployed. The world (including the rogue nations like North Korea and China) realizes that ONE nuke exploded means the end of the world.
YOU CAN'T GET MUCH SAFER THAN THAT.
And do you REALLY think that Russia, China, North Korea and Pakistan will give up their nukes?
Or are you imaging that they will disarm if American unilaterally gives up our nukes?