Nonproliferation and the Budapest Memorandum

While I found Bill Sweet’s article “France’s Oppenheimer ” (Physics Today, March 2025, page 46) informative and entertaining, I also find it necessary to correct a serious omission in the final paragraph. South Africa is not the only nuclear-armed state to have given up its arsenal. Belarus, Kazakhstan, and Ukraine gave up the nuclear weapons left in their lands following the breakup of the Soviet Union.

Indeed, when the Soviet Union collapsed, Ukraine held the world’s third-largest arsenal of nuclear weapons. It denuclearized voluntarily and joined the Treaty on the Non-Proliferation of Nuclear Weapons in 1994. In return, the US, the UK, and the Russian Federation signed the Budapest Memorandum, in which they committed to, among other things, “respect the independence and sovereignty and the existing borders of Ukraine,” “refrain from the threat or use of force against the territorial integrity or political independence of Ukraine,” and “refrain from economic coercion designed to subordinate to their own interest the exercise by Ukraine of the rights inherent in its sovereignty.” ¹

Russia’s forced annexation of Crimea in 2014, followed shortly by its promotion of separatist activities in the Donetsk and Luhansk territories, and later its full-scale invasion of Ukraine starting in 2022 violated the Budapest Memorandum. And now doubts among US allies as to the reliability of US security commitments threaten to cause other nations to become nuclear states. ^{2 , 3}