The principle of Mutually Assured Destruction makes war less likely.  States are fundamentally rational, and as such, nuclear proliferation has generally made war less likely, by promulgating the principle of mutually assured destruction (MAD).  States go to war with other states when they think they can win the conflict they will provoke. By making victory impossible, MAD makes wars unprofitable, and thereby prevents them from beginning in the first place. The Cold War never turned hot partially for this reason, and it is possible that the Israeli-Iranian relationship could be stabilized by both states possessing a nuclear deterrent. North Korea may well desire to Nuke the United States and Japan, and may well feel that there would be no moral issues with doing so, but they have refrained from doing so. As they have refrained from invading the South since 1950. There is substantial evidence that even the most irrational regimes can be deterred. No matter how dictatorial and authoritarian a state government, the prospect of complete nuclear annihilation will be effective in restraining its ambitions. [1]  In the case of Iran, the threat to Iranian cities by the Iraqi army moving on to the offensive and using chemical weapons motivated Khomeini to make peace in 1988. [2] It is worth noting that they have not explicitly attacked Israel themselves, preferring to work through proxies. It would seem unlikely that Iran, if it were to become the only nuclear power in the Islamic world, could avoid responsibility if Hamas or Hezbollah were to utilize a weapon.  [1] Kenneth Waltz, “The Spread of Nuclear Weapons: More May Better,” I, Number 171 (London: International Institute for Strategic Studies, 1981),   [2] Globalsecurity.org, ‘Iran-Iraq War (1980-1988)’,