When the Soviet Union broke up in 1991, there were thousands of former Soviet nuclear warheads, as well as hundreds of intercontinental ballistic missiles and bombers, left on Ukraine’s territory, which it decided to transfer to Russia. Ukraine never had an independent nuclear weapons arsenal, or control over these weapons, but agreed to remove former Soviet weapons stationed on its territory. In 1992, Ukraine signed the Lisbon Protocol and it joined the Nuclear Non-Proliferation Treaty as a non-nuclear weapon state in 1994. The transfer of all nuclear material took some time, but by 2001, all nuclear weapons had been transferred to Russia to be dismantled and all launch silos decommissioned.

While some may ask if Russia would have invaded Ukraine if it still had Soviet nuclear weapons stationed on its territory, there is little convincing historical evidence that the possession or presence of nuclear weapons definitively prevents conflict, when many other variables may be considered, including the prohibition of the use of force under the UN Charter or even just luck. Even beyond this, it is not clear that Ukraine would have been able to take control of former Soviet nuclear weapons, technically or politically. What we do know is that the possession of nuclear weapons by Russia and the United States clearly has not prevented the threat of conflict between Russia and a U.S. ally or the potential humanitarian consequences of any conflict for civilians in the region. Read more about Ukraine and nuclear weapons.