Every country can try and start a nuclear program if they'd like, as long as no one is stopping them. If you have power, and sway, then you can do what you like. AKA have nuclear weapons and tell others not to have nuclear weapons. That being said, every country would like to be the only country with nuclear weapons, thats just not going to happen, but when a radical country makes strides, it becomes a threat to every other country. If someone or something is threatened, and has the power to do something about it, they're going to.