Deterrence indeed; the nations keenest right now on developing their own nuclear weapons (DPRK and Iran, I'm looking at you) are doing it because they know damn well it's the only way to be safe from the world's current invasion-happy globe-trotting nation and favoured sidekick (who, to be fair, do seem a lot less keen to invade other countries after the long series of monumental clusterfucks in Iraq and Afghanistan). The question is can they develop them before said warstarters decide to invade anyway?
China remembers what the US was thinking the last time it was yomping about near the Yalu River and certainly won't put up with anyone invading the DPRK, so they're safe at least from that quarter, but if I was Iran, having watched Iraq get invaded and then screwed over for a decade for essentially no reason whatsoever, I'd be really keen to have some kind of deterrence before the US decided to invade.
China remembers what the US was thinking the last time it was yomping about near the Yalu River and certainly won't put up with anyone invading the DPRK, so they're safe at least from that quarter, but if I was Iran, having watched Iraq get invaded and then screwed over for a decade for essentially no reason whatsoever, I'd be really keen to have some kind of deterrence before the US decided to invade.