The best way to get Iran to follow the example of its next door neighbour Pakistan, and its slightly more distant neighbour Israel, and seek to develop nuclear weapons is to threaten it with attack.

And the best way to discourage that would be for the USA (preferably jointly with the EU, and Russia ) to guarantee that there will be no attack on Iran, and that any such attack would be treated as a hostile act by the guarantors. And make that guarantee conditional on Iran not developing nuclear weapons.

And if it really was just a matter of preventing nuclear proliferation that would happen. But its not.
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It's worth pointing out that the Scottish Nationalists hope to bring about a situation in which there will no longer be any United Kingdom.