How could you leave out NK?  Iran wouldnt Nuke anyone for the same reason no one else uses nukes. MAD. They would only ensure their own destruction.  The shitty reality of the real world is that nukes are the only surefire way to prevent invasion. If Ukraine never gave up their nukes, they wouldnt be in their current mess. The reason no one has attacked or invaded the insane assholes in NK, is nukes. If Iran had nukes, they wouldnt be getting bombed right now.  Many nuclear armed countries threaten to use their nukes all the time, and threaten their enemies with total and complete destruction.  But they know they cant act on it without being completely destroyed themselves.