I see the following factors as important in convincing countries to get nukes or keep them:

1) The West enabling the assassination (by torture) of Khadaffi of Libya after having given Khadaffi a guarantee of proteciton in return for giving up his (and Saddam's) WMD programs. BTW, that's how the A.Q.Khan nuclear proliferation for profit operation was discovered. Hillary Clinton bragged about the operation, paraphrasing Caesar: "We came, we saw, he died."

2) Ukraine being attacked by Russia after giving up its inherited nuclear weapons, in return for security guaranties from Russia, US and Britain. Ukraine's lack of nukes, and Russia's possession of the, both contributed to the course of the war. If Ukraine had nukes (and had it not given them up, it wold have), Russia wouldn't have attacked. If Russia didn't have nukes, NATO would have obliterated the Russian invasion troops in a matter of days.

3) North Korea developing not only nukes, but a credible nuclear deterrent, without anyone trying to stop them.

4) Israel's ability to deter serious attacks (so far) because of its unacknowledged decades long possession of deliverable nukes.