South Africa was once a nuclear power in the sense that it developed and possessed nuclear weapons. It is the only country to have voluntarily dismantled its entire nuclear weapons program. South Africa built six nuclear weapons in the 1980s but dismantled them in the early 1990s before joining the Treaty on the Non-Proliferation of Nuclear Weapons (NPT) as a non-nuclear weapon state. Since then, South Africa has not maintained a nuclear weapons program but does maintain a significant nuclear energy infrastructure for peaceful purposes.
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