Following the break-up of the Soviet Union, Ukraine inherited the Soviet-era atomic weapons on its soil and became - for a few years - the world's third biggest nuclear power. After months of tense diplomacy, the newly independent Ukraine agreed to give up the weapons in return for what were termed "assurances" about its future security and territorial integrity. These "assurances" were agreed by Russia, the USA and Britain in the Budapest Memorandum, signed in December 1994. They are now controversial given the Russian invasion of Crimea in 2014 and then the rest of Ukraine in 2022. Louise Hidalgo talks to Steven Pifer, a senior American diplomat involved in the talks.

PHOTO: Pro-Ukrainian demonstrators in London in 2022 (Getty Images)