As of today, states in possession of nuclear weapons include the United States, Russia, United Kingdom, France, China, India, Pakistan, North Korea and Israel (although Israel doesn't publicly acknowledge its nuclear weapons).
Will another nation be added to this list before 2025 by one of the follow actions?
Conducting a nuclear weapon test
Employing a nuclear weapon
Official government statements explicitly claiming possession of nuclear weapons
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@DavidFWatson An extremely good point raised here.
Any new nation would need to have sovereign control of nuclear weapons to count as "possession" under this question. Under current NATO agreements, the US "maintains absolute control and custody of their nuclear weapons forward-deployed in Europe." For the purposes of this question, NATO stationing of weapons in a new country under current agreements does not equate to possession. https://www.nato.int/cps/en/natohq/topics_50068.htm
Similarly, stationing of Russian nuclear weapons in Belarus doesn't count as possession given those weapons remain under Russian control.
@EvanDaniel No, but it does need to be an official statement from the government stating unequivocally that the nation possesses nuclear weapons. This covers the case of, for example, the US providing South Korea weapons where they would not need to perform a test for credibility.