https://en.wikipedia.org/wiki/Treaty_on_the_Non-Proliferation_of_Nuclear_Weapons
The Treaty on the Non-Proliferation of Nuclear Weapons, commonly known as the Non-Proliferation Treaty or NPT, is an international treaty whose objective is to prevent the spread of nuclear weapons and weapons technology, to promote cooperation in the peaceful uses of nuclear energy, and to further the goal of achieving nuclear disarmament and general and complete disarmament.[1]

Opened for signature in 1968, the Treaty entered into force in 1970. On 11 May 1995, the Treaty was extended indefinitely. More countries have adhered to the NPT than any other arms limitation and disarmament agreement, a testament to the Treaty's significance.[1] A total of 191 states have joined the Treaty, though North Korea, which acceded to the NPT in 1985 but never came into compliance, announced its withdrawal in 2003.[2] Four UN member states have never joined the NPT: India, Israel, Pakistan and South Sudan.

The treaty recognizes five states as nuclear-weapon states: the United States, Russia, the United Kingdom, France, and China (also the five permanent members of the United Nations Security Council). Four other states are known or believed to possess nuclear weapons: India, Pakistan and North Korea have openly tested and declared that they possess nuclear weapons, while Israel has had a policy of opacity regarding its nuclear weapons program.

The NPT consists of a preamble and eleven articles. Although the concept of "pillars" is not expressed anywhere in the NPT, the treaty is nevertheless sometimes interpreted as a three-pillar system, with an implicit balance among them:

non-proliferation,
disarmament, and
the right to peacefully use nuclear technology.[3]

"and to further the goal of achieving nuclear disarmament and general and complete disarmament." is the important bit. At some stage someone has to move on achieving that. Name me one situation where sending a Nuke or rather nukes off would actually achieve anything. The ones we have are controlled by USA anyway so we need authorisation from them to fire one. Lets just suppose a terrorist Org actually managed to Nuke us. Who would we fire back at? If the backpackers in 7/11 were carrying nukes who would we fire back at? If the 9/11 planes had been loaded with nukes who would the US have fired back at?......No One because you would kill millions of inocent civillions trying to kill a handfull of terrorists. Nukes are unusable, fine they were OK to face off Russia in the cold war but that was then and this is now. Russia and the US still have enough Nukes to kill the world 3 times over. If they ever kick off were all dead anyway. In fact our only slim chance of survival in that senario is not to have Nukes. Russia would bother nuking us and US and Russia can reduce the worlds population amoungst themselves. We need to put our money into conventional forces that can actually combat terrorists if needed. So far our conventional forces interventions in Iraq, Have produced nothing but dead people and millions fleeing the fighting as ISIS pushes north into Syria in search of their fabled last battle against the infidel and that was all for oil, not removing Saddam Hussain. You cant beat religious radicals ie ISIS by bombing them, its impossible. The only people that end up getting hurt are civillians. Thousands more will join them because they are all under the misguided thinking that there is a god and they will be going upstairs to meet him. Sorry guys hate to break this to you but your wrong.

http://www.un.org/disarmament/WMD/Nuclear/NPT.shtml

As an addition there are hundreds of countries that dont have Nuclear Weapons including Australia. They are not being invaded or bombed by those that do.

https://en.wikipedia.org/wiki/Nuclear-weapon-free_zone

http://www.armscontrol.org/factsheets/Nuclearweaponswhohaswhat
Nuclear-Weapon States:
The nuclear-weapon states (NWS) are the five states—China, France, Russia, United Kingdom, and the United States—officially recognized as possessing nuclear weapons by the NPT. Although the treaty legitimizes these states’ nuclear arsenals, it also establishes that they are not supposed to build and maintain such weapons in perpetuity. Article VI of the treaty holds that each state-party is to “pursue negotiations in good faith on effective measures relating to cessation of the nuclear arms race at an early date and to nuclear disarmament.” In 2000, the five NWS committed themselves to an “unequivocal undertaking…to accomplish the total elimination of their nuclear arsenals.” But for now, the five continue to retain the bulk of their nuclear forces. Because of the secretive nature with which most governments treat information about their nuclear arsenals, most of the figures below are best estimates of each nuclear-weapon state’s nuclear holdings, including both strategic warheads and lower-yield devices referred to as tactical weapons. Russia and the United States also retain thousands of retired warheads planned for dismantlement, not included here.

If these weapons were used even in a “limited” way, the result would be catastrophic nuclear devastation.

And as they say many a true word spoken in jest