I'll make it very short.
Looking at the rationale for countries to go nuclear, we saw that India and Pakistan have already gone nuclear, so they are a huge concern. North Korea has gone nuclear, so they're a huge concern. Iran looks set to follow suit. Were there misguided policies that led India and Pakistan and North Korea to go nuclear? Possibly. Compare that with the approach that was taken with the Ukraine, Belarus, and Kazakhstan, all of which inherited nuclear weapons and could quite easily have become nuclear weapon states. Very intense, very successful diplomatic initiatives got them to give up the nuclear weapons they possessed.
As I mentioned before, a combination of diplomacy and sanctions can be more successful than just sanctions, particularly on a state that's very powerful and has the possibility of developing its own nuclear arsenal. As we saw with North Korea, the sanctions didn't work. They went with nuclear weapons, but they are very interested in the possibility of a nuclear-weapon-free zone that would have security assurances.
What is Iran calling for? Attention on Israel's nuclear weapons. So they were supportive of a packaged approach that included non-proliferation, that was directed against them, as long as it included Israel's nuclear weapons in the Middle East process for a nuclear-weapon-free zone.