We had the first one and we were the first to use it. And continue to threaten to use it again.
Russia and China got it to warn us not to think this country could win a war against them in the future. And that's the rationale why Iran would want nuclear weapons as well. They saw what happened to Afghanistan and Iraq. They will not be invaded and conquered.
Even Brazil.
http://www.spiegel.de/international/world/0,1518,693336,00.html#ref=rssBrazil is probably also developing something else in the plants it has declared as production facilities for nuclear submarines: nuclear weapons. Vice President José Alencar offered a reason when he openly advocated Brazil's acquisition of nuclear weapons in September 2009. For a country with a 15,000-kilometer border and rich offshore oil reserves, Alencar says, these weapons would not only be an important tool of "deterrence," but would also give Brazil the means to increase its importance on the international stage. When it was pointed out that Brazil had signed the NPT, Alencar reacted calmly, saying it was "a matter that was open to negotiation."
France, India, Pakistan, and Israel have their own issues concerning their insecurity of sovereignty exclusive of this country. But obviously, they have witnessed how other countries will treat you if you have nuclear weapons or think you do.