As the NY Times point out in their review of two upcoming histories of The Bomb, Robbert Oppenheimer originally assumed that little could stop anyone from developing nuclear weapons. Thankfully, he was wrong.
With a geek's typical hubris, Oppenheimer assumed that since the laws of physics were universal, very little could stop anyone in getting a nuclear weapon, given the time and resources. Alas, the time and resources needed are indeed scarce, so to this day, only nine countries are nuclear-equipped—the United States, Russia, United Kingdom, France, China, India, Pakistan, North Korea and Israel. Here we see these links visualised, starting with the Manhattan project and fanning out over the last six decades (click here for the full-size popup).
Instead, three proliferation experts demonstrate how nuclear capabilities were passed as political bargaining chips, stolen via espionage, and limited with diplomacy. Both books seem like fascinating reads. Check out much more at the Times: [NYTimes]