Iran signed the Nuclear Non-Proliferation Treaty in 1968. Currently they are likely in breach of the treaty (non-cooperation) which is what all the fuss is about.
Israel, India, Pakistan never signed it. North Korean withdrew from it in 2003. South Africa joined in 1991 and dismantled its weapons.
“The impetus behind the NPT was concern for the safety of a world with many nuclear weapon states. It was recognized that the cold war deterrent relationship between just the United States and Soviet Union was fragile. Having more nuclear nuclear-weapon states would reduce security for all, multiplying the risks of miscalculation, accidents, unauthorized use of weapons, or from escalation in tensions, nuclear conflict.”
Source
http://en.wikipedia.org/wiki/Nuclear_Non-Proliferation_Treaty
EDIT
ohnohesback – Member
How would we feel if we had to develop our nuclear facilities along the lines set by, and offer them up to, inspection by Iran?
We do; under the terms of the NPT all our nuclear facilities, peaceful or other wise, are open to inspection to the IAEA.